<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:6791e5dc-39d0-47a9-bea6-03fe8aa5ac6d,g:eea94d03-f3a2-42e4-9d58-3d81272d0839-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://www.fortrea.com/role/COVER" xlink:type="simple" xlink:href="ftre-20251231.xsd#COVER"/>
  <link:definitionLink xlink:role="http://www.fortrea.com/role/COVER" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationLineItems_1bc891c0-cd1c-48f5-b5ed-4aad4b1a3933" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationTable_5437741c-f3ad-46ba-89d6-bba027f30d39" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentInformationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_DocumentInformationLineItems_1bc891c0-cd1c-48f5-b5ed-4aad4b1a3933" xlink:to="loc_dei_DocumentInformationTable_5437741c-f3ad-46ba-89d6-bba027f30d39" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_5904abe4-8223-405d-8ac2-361dba08c4de" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_DocumentInformationTable_5437741c-f3ad-46ba-89d6-bba027f30d39" xlink:to="loc_us-gaap_StatementClassOfStockAxis_5904abe4-8223-405d-8ac2-361dba08c4de" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_5904abe4-8223-405d-8ac2-361dba08c4de_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_5904abe4-8223-405d-8ac2-361dba08c4de" xlink:to="loc_us-gaap_ClassOfStockDomain_5904abe4-8223-405d-8ac2-361dba08c4de_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_3a99f202-c9da-4aa1-999b-2ce744b0f5cb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_5904abe4-8223-405d-8ac2-361dba08c4de" xlink:to="loc_us-gaap_ClassOfStockDomain_3a99f202-c9da-4aa1-999b-2ce744b0f5cb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_4c037919-949a-4c17-a4b1-0af37e1d92c3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_3a99f202-c9da-4aa1-999b-2ce744b0f5cb" xlink:to="loc_us-gaap_CommonStockMember_4c037919-949a-4c17-a4b1-0af37e1d92c3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredClassAMember_9127b95c-9bef-4a07-a1db-5058c988a3e7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PreferredClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_3a99f202-c9da-4aa1-999b-2ce744b0f5cb" xlink:to="loc_us-gaap_PreferredClassAMember_9127b95c-9bef-4a07-a1db-5058c988a3e7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_ababcb5e-4fa7-4e00-8921-4fe677ccc485" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentType"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_1bc891c0-cd1c-48f5-b5ed-4aad4b1a3933" xlink:to="loc_dei_DocumentType_ababcb5e-4fa7-4e00-8921-4fe677ccc485" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentAnnualReport_cbe818b6-bf66-4757-a23b-adfc0e96d40d" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentAnnualReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_1bc891c0-cd1c-48f5-b5ed-4aad4b1a3933" xlink:to="loc_dei_DocumentAnnualReport_cbe818b6-bf66-4757-a23b-adfc0e96d40d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CurrentFiscalYearEndDate_c49109df-90c7-40e4-95ed-a11e8ab2f958" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_CurrentFiscalYearEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_1bc891c0-cd1c-48f5-b5ed-4aad4b1a3933" xlink:to="loc_dei_CurrentFiscalYearEndDate_c49109df-90c7-40e4-95ed-a11e8ab2f958" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_3777e68e-7c43-4022-a794-684e00de99d2" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentPeriodEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_1bc891c0-cd1c-48f5-b5ed-4aad4b1a3933" xlink:to="loc_dei_DocumentPeriodEndDate_3777e68e-7c43-4022-a794-684e00de99d2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentTransitionReport_88f1404f-7f06-4d86-9407-fafc6a87e5b3" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentTransitionReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_1bc891c0-cd1c-48f5-b5ed-4aad4b1a3933" xlink:to="loc_dei_DocumentTransitionReport_88f1404f-7f06-4d86-9407-fafc6a87e5b3" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_dba56533-9cee-479b-a3f3-82b620176fd5" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityFileNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_1bc891c0-cd1c-48f5-b5ed-4aad4b1a3933" xlink:to="loc_dei_EntityFileNumber_dba56533-9cee-479b-a3f3-82b620176fd5" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_24e13468-011b-48b1-b176-471b91c1d02d" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityRegistrantName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_1bc891c0-cd1c-48f5-b5ed-4aad4b1a3933" xlink:to="loc_dei_EntityRegistrantName_24e13468-011b-48b1-b176-471b91c1d02d" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_28dbcf5c-8fa9-4e80-8d60-8ba561c706f6" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityIncorporationStateCountryCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_1bc891c0-cd1c-48f5-b5ed-4aad4b1a3933" xlink:to="loc_dei_EntityIncorporationStateCountryCode_28dbcf5c-8fa9-4e80-8d60-8ba561c706f6" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_d9b8f887-bfeb-4877-825d-7f40f6a68c9f" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityTaxIdentificationNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_1bc891c0-cd1c-48f5-b5ed-4aad4b1a3933" xlink:to="loc_dei_EntityTaxIdentificationNumber_d9b8f887-bfeb-4877-825d-7f40f6a68c9f" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_44944565-2c4f-4c56-9ca9-cafac96a061b" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressAddressLine1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_1bc891c0-cd1c-48f5-b5ed-4aad4b1a3933" xlink:to="loc_dei_EntityAddressAddressLine1_44944565-2c4f-4c56-9ca9-cafac96a061b" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_9ec0155f-70b4-4bb3-bb67-3e1538acc8c0" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressCityOrTown"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_1bc891c0-cd1c-48f5-b5ed-4aad4b1a3933" xlink:to="loc_dei_EntityAddressCityOrTown_9ec0155f-70b4-4bb3-bb67-3e1538acc8c0" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_ec9c539b-f641-4861-9083-059424edc7e3" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressStateOrProvince"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_1bc891c0-cd1c-48f5-b5ed-4aad4b1a3933" xlink:to="loc_dei_EntityAddressStateOrProvince_ec9c539b-f641-4861-9083-059424edc7e3" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_d33476ab-ae1c-4056-81de-9b9c9a98384d" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressPostalZipCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_1bc891c0-cd1c-48f5-b5ed-4aad4b1a3933" xlink:to="loc_dei_EntityAddressPostalZipCode_d33476ab-ae1c-4056-81de-9b9c9a98384d" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_6975955b-e005-4418-b34a-e02105fe77a1" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_CityAreaCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_1bc891c0-cd1c-48f5-b5ed-4aad4b1a3933" xlink:to="loc_dei_CityAreaCode_6975955b-e005-4418-b34a-e02105fe77a1" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_27dfbfd5-3c72-40af-bc64-9c7a15c3765c" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_LocalPhoneNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_1bc891c0-cd1c-48f5-b5ed-4aad4b1a3933" xlink:to="loc_dei_LocalPhoneNumber_27dfbfd5-3c72-40af-bc64-9c7a15c3765c" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_b4e04624-73b3-4810-b235-3bc50ea01df3" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_Security12bTitle"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_1bc891c0-cd1c-48f5-b5ed-4aad4b1a3933" xlink:to="loc_dei_Security12bTitle_b4e04624-73b3-4810-b235-3bc50ea01df3" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_7a02e1d7-ca35-43ae-abb0-15c94da8d1ff" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_TradingSymbol"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_1bc891c0-cd1c-48f5-b5ed-4aad4b1a3933" xlink:to="loc_dei_TradingSymbol_7a02e1d7-ca35-43ae-abb0-15c94da8d1ff" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_e1559564-566b-4829-a72a-d14c4580bba3" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_SecurityExchangeName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_1bc891c0-cd1c-48f5-b5ed-4aad4b1a3933" xlink:to="loc_dei_SecurityExchangeName_e1559564-566b-4829-a72a-d14c4580bba3" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_NoTradingSymbolFlag_1c50e83d-5d92-48e5-98c0-5b98e682b73f" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_NoTradingSymbolFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_1bc891c0-cd1c-48f5-b5ed-4aad4b1a3933" xlink:to="loc_dei_NoTradingSymbolFlag_1c50e83d-5d92-48e5-98c0-5b98e682b73f" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityWellKnownSeasonedIssuer_b65caac7-aaf1-4805-8442-f81f7616199d" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityWellKnownSeasonedIssuer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_1bc891c0-cd1c-48f5-b5ed-4aad4b1a3933" xlink:to="loc_dei_EntityWellKnownSeasonedIssuer_b65caac7-aaf1-4805-8442-f81f7616199d" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityVoluntaryFilers_a95c4b8a-994c-4c52-b02e-47d89fcf410a" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityVoluntaryFilers"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_1bc891c0-cd1c-48f5-b5ed-4aad4b1a3933" xlink:to="loc_dei_EntityVoluntaryFilers_a95c4b8a-994c-4c52-b02e-47d89fcf410a" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCurrentReportingStatus_685c9d58-d2f2-41c4-8288-c73e2112f2eb" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityCurrentReportingStatus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_1bc891c0-cd1c-48f5-b5ed-4aad4b1a3933" xlink:to="loc_dei_EntityCurrentReportingStatus_685c9d58-d2f2-41c4-8288-c73e2112f2eb" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInteractiveDataCurrent_69cb374c-9ff7-4b45-9b59-883f7298c919" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityInteractiveDataCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_1bc891c0-cd1c-48f5-b5ed-4aad4b1a3933" xlink:to="loc_dei_EntityInteractiveDataCurrent_69cb374c-9ff7-4b45-9b59-883f7298c919" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFilerCategory_5380ef71-33fc-4fd6-822e-b3e4406a97a1" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityFilerCategory"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_1bc891c0-cd1c-48f5-b5ed-4aad4b1a3933" xlink:to="loc_dei_EntityFilerCategory_5380ef71-33fc-4fd6-822e-b3e4406a97a1" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitySmallBusiness_c31333bd-a99c-4bed-8f37-010ef718def8" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntitySmallBusiness"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_1bc891c0-cd1c-48f5-b5ed-4aad4b1a3933" xlink:to="loc_dei_EntitySmallBusiness_c31333bd-a99c-4bed-8f37-010ef718def8" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_431eec8d-009f-4699-b2b6-df86a46beed0" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityEmergingGrowthCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_1bc891c0-cd1c-48f5-b5ed-4aad4b1a3933" xlink:to="loc_dei_EntityEmergingGrowthCompany_431eec8d-009f-4699-b2b6-df86a46beed0" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_IcfrAuditorAttestationFlag_c81f92ca-cff3-4505-9f3f-c69f88aee6fb" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_IcfrAuditorAttestationFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_1bc891c0-cd1c-48f5-b5ed-4aad4b1a3933" xlink:to="loc_dei_IcfrAuditorAttestationFlag_c81f92ca-cff3-4505-9f3f-c69f88aee6fb" xlink:type="arc" order="26"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFinStmtErrorCorrectionFlag_c0c2a9e9-af20-41f5-b534-f5c45bc5daed" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentFinStmtErrorCorrectionFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_1bc891c0-cd1c-48f5-b5ed-4aad4b1a3933" xlink:to="loc_dei_DocumentFinStmtErrorCorrectionFlag_c0c2a9e9-af20-41f5-b534-f5c45bc5daed" xlink:type="arc" order="27"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityShellCompany_5ebfbc20-bd9a-43ac-b553-ac75ab1413a0" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityShellCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_1bc891c0-cd1c-48f5-b5ed-4aad4b1a3933" xlink:to="loc_dei_EntityShellCompany_5ebfbc20-bd9a-43ac-b553-ac75ab1413a0" xlink:type="arc" order="28"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityPublicFloat_1f80a8d3-0e20-4751-83bb-e742be0386b3" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityPublicFloat"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_1bc891c0-cd1c-48f5-b5ed-4aad4b1a3933" xlink:to="loc_dei_EntityPublicFloat_1f80a8d3-0e20-4751-83bb-e742be0386b3" xlink:type="arc" order="29"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCommonStockSharesOutstanding_0bc11033-7919-43dd-8677-641d67ecfaa5" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityCommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_1bc891c0-cd1c-48f5-b5ed-4aad4b1a3933" xlink:to="loc_dei_EntityCommonStockSharesOutstanding_0bc11033-7919-43dd-8677-641d67ecfaa5" xlink:type="arc" order="30"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentsIncorporatedByReferenceTextBlock_db6baee8-9c2d-4901-8fbf-fff2e8014057" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentsIncorporatedByReferenceTextBlock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_1bc891c0-cd1c-48f5-b5ed-4aad4b1a3933" xlink:to="loc_dei_DocumentsIncorporatedByReferenceTextBlock_db6baee8-9c2d-4901-8fbf-fff2e8014057" xlink:type="arc" order="31"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_0b6b2f0c-3211-4be2-9cae-477a30f4716f" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityCentralIndexKey"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_1bc891c0-cd1c-48f5-b5ed-4aad4b1a3933" xlink:to="loc_dei_EntityCentralIndexKey_0b6b2f0c-3211-4be2-9cae-477a30f4716f" xlink:type="arc" order="32"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalYearFocus_a5516d71-6085-455f-a858-1c3a13c82151" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentFiscalYearFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_1bc891c0-cd1c-48f5-b5ed-4aad4b1a3933" xlink:to="loc_dei_DocumentFiscalYearFocus_a5516d71-6085-455f-a858-1c3a13c82151" xlink:type="arc" order="33"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalPeriodFocus_3545f0f5-3310-4bf6-9362-83d8db7be3ac" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentFiscalPeriodFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_1bc891c0-cd1c-48f5-b5ed-4aad4b1a3933" xlink:to="loc_dei_DocumentFiscalPeriodFocus_3545f0f5-3310-4bf6-9362-83d8db7be3ac" xlink:type="arc" order="34"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_86ee8ed3-efc8-48fc-9411-af10e1e29261" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_AmendmentFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_1bc891c0-cd1c-48f5-b5ed-4aad4b1a3933" xlink:to="loc_dei_AmendmentFlag_86ee8ed3-efc8-48fc-9411-af10e1e29261" xlink:type="arc" order="35"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fortrea.com/role/CONSOLIDATEDANDCOMBINEDSTATEMENTSOFOPERATIONSParenthetical" xlink:type="simple" xlink:href="ftre-20251231.xsd#CONSOLIDATEDANDCOMBINEDSTATEMENTSOFOPERATIONSParenthetical"/>
  <link:definitionLink xlink:role="http://www.fortrea.com/role/CONSOLIDATEDANDCOMBINEDSTATEMENTSOFOPERATIONSParenthetical" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_35d07ccb-5505-4086-a080-c070cfe01e89" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_d68029f2-74d3-4e25-9ff8-7d96e4096716" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_35d07ccb-5505-4086-a080-c070cfe01e89" xlink:to="loc_us-gaap_StatementTable_d68029f2-74d3-4e25-9ff8-7d96e4096716" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_594f8447-bf60-4f0c-878d-8df15d755183" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_d68029f2-74d3-4e25-9ff8-7d96e4096716" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_594f8447-bf60-4f0c-878d-8df15d755183" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_594f8447-bf60-4f0c-878d-8df15d755183_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_594f8447-bf60-4f0c-878d-8df15d755183" xlink:to="loc_us-gaap_RelatedPartyDomain_594f8447-bf60-4f0c-878d-8df15d755183_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_675f059b-c366-4bca-92d8-47534a01d30c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_594f8447-bf60-4f0c-878d-8df15d755183" xlink:to="loc_us-gaap_RelatedPartyDomain_675f059b-c366-4bca-92d8-47534a01d30c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_d0f54306-2a07-4452-8fd0-487cd032b79f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_675f059b-c366-4bca-92d8-47534a01d30c" xlink:to="loc_us-gaap_RelatedPartyMember_d0f54306-2a07-4452-8fd0-487cd032b79f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServiceExcludingDepreciationDepletionAndAmortization_8ed13e0c-8bd2-49a0-bc5b-1246ded5469b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CostOfGoodsAndServiceExcludingDepreciationDepletionAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_35d07ccb-5505-4086-a080-c070cfe01e89" xlink:to="loc_us-gaap_CostOfGoodsAndServiceExcludingDepreciationDepletionAndAmortization_8ed13e0c-8bd2-49a0-bc5b-1246ded5469b" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fortrea.com/role/CONSOLIDATEDANDCOMBINEDSTATEMENTSOFCHANGESINEQUITY" xlink:type="simple" xlink:href="ftre-20251231.xsd#CONSOLIDATEDANDCOMBINEDSTATEMENTSOFCHANGESINEQUITY"/>
  <link:definitionLink xlink:role="http://www.fortrea.com/role/CONSOLIDATEDANDCOMBINEDSTATEMENTSOFCHANGESINEQUITY" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_09c3c3ba-dc43-4976-9a97-cc30efc7bbef" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_f933e8d2-9af7-4bb7-8bd6-19cb3cdd5287" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_09c3c3ba-dc43-4976-9a97-cc30efc7bbef" xlink:to="loc_us-gaap_StatementTable_f933e8d2-9af7-4bb7-8bd6-19cb3cdd5287" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_e683a602-40ba-43c8-b1f2-c974fdd34164" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_f933e8d2-9af7-4bb7-8bd6-19cb3cdd5287" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_e683a602-40ba-43c8-b1f2-c974fdd34164" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_e683a602-40ba-43c8-b1f2-c974fdd34164_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_e683a602-40ba-43c8-b1f2-c974fdd34164" xlink:to="loc_us-gaap_EquityComponentDomain_e683a602-40ba-43c8-b1f2-c974fdd34164_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_0e766660-bab8-458c-8a68-1a437d79702a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_e683a602-40ba-43c8-b1f2-c974fdd34164" xlink:to="loc_us-gaap_EquityComponentDomain_0e766660-bab8-458c-8a68-1a437d79702a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_1e7fdf6f-c02d-4b96-80c8-f825dd53c070" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_0e766660-bab8-458c-8a68-1a437d79702a" xlink:to="loc_us-gaap_CommonStockMember_1e7fdf6f-c02d-4b96-80c8-f825dd53c070" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_fe3a2340-550a-4f22-8329-1373d9aab09a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_0e766660-bab8-458c-8a68-1a437d79702a" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_fe3a2340-550a-4f22-8329-1373d9aab09a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_ParentCompanyInvestmentMember_ff7fdbe7-77ca-49c5-b65e-eaa2ad5e22f2" xlink:href="ftre-20251231.xsd#ftre_ParentCompanyInvestmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_0e766660-bab8-458c-8a68-1a437d79702a" xlink:to="loc_ftre_ParentCompanyInvestmentMember_ff7fdbe7-77ca-49c5-b65e-eaa2ad5e22f2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_af20441c-3cc0-4c87-adc6-149cdd91c3d7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_0e766660-bab8-458c-8a68-1a437d79702a" xlink:to="loc_us-gaap_RetainedEarningsMember_af20441c-3cc0-4c87-adc6-149cdd91c3d7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_ed123973-a4d6-443a-ad50-010cba707e9e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_0e766660-bab8-458c-8a68-1a437d79702a" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_ed123973-a4d6-443a-ad50-010cba707e9e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_1ebd677e-4e54-40a4-ac7d-3be416719de2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_09c3c3ba-dc43-4976-9a97-cc30efc7bbef" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_1ebd677e-4e54-40a4-ac7d-3be416719de2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_951c4bbc-f4e1-4698-b0f1-b065c8fef5ce" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_1ebd677e-4e54-40a4-ac7d-3be416719de2" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_951c4bbc-f4e1-4698-b0f1-b065c8fef5ce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_4a732a3f-b98e-4a84-be7f-c80ac842b3cf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_1ebd677e-4e54-40a4-ac7d-3be416719de2" xlink:to="loc_us-gaap_StockholdersEquity_4a732a3f-b98e-4a84-be7f-c80ac842b3cf" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_00d5f373-8770-4168-9d09-c269496a4b76" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_1ebd677e-4e54-40a4-ac7d-3be416719de2" xlink:to="loc_us-gaap_NetIncomeLoss_00d5f373-8770-4168-9d09-c269496a4b76" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_93c283d0-69f6-4aeb-8b54-938e744e4766" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_1ebd677e-4e54-40a4-ac7d-3be416719de2" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_93c283d0-69f6-4aeb-8b54-938e744e4766" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_NetTransfersToParentSpecialPayment_d370380f-4393-41c3-a5fd-38b65e304b28" xlink:href="ftre-20251231.xsd#ftre_NetTransfersToParentSpecialPayment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_1ebd677e-4e54-40a4-ac7d-3be416719de2" xlink:to="loc_ftre_NetTransfersToParentSpecialPayment_d370380f-4393-41c3-a5fd-38b65e304b28" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_NetTransfersFromToParentExcludingSpecialPayment_0ee06846-685d-4c7f-82a5-2e039349de93" xlink:href="ftre-20251231.xsd#ftre_NetTransfersFromToParentExcludingSpecialPayment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_1ebd677e-4e54-40a4-ac7d-3be416719de2" xlink:to="loc_ftre_NetTransfersFromToParentExcludingSpecialPayment_0ee06846-685d-4c7f-82a5-2e039349de93" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_AdjustmentsToAdditionalPaidInCapitalFormerParentInvestmentReclassification_cd020ae6-7313-40a4-9bc1-8761b9df7f00" xlink:href="ftre-20251231.xsd#ftre_AdjustmentsToAdditionalPaidInCapitalFormerParentInvestmentReclassification"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_1ebd677e-4e54-40a4-ac7d-3be416719de2" xlink:to="loc_ftre_AdjustmentsToAdditionalPaidInCapitalFormerParentInvestmentReclassification_cd020ae6-7313-40a4-9bc1-8761b9df7f00" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_9e8a0251-a919-41c7-bffe-11271c85e8b5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_1ebd677e-4e54-40a4-ac7d-3be416719de2" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesNewIssues_9e8a0251-a919-41c7-bffe-11271c85e8b5" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_cb642cfb-a5cd-4b41-af1b-075720fd8909" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodValueNewIssues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_1ebd677e-4e54-40a4-ac7d-3be416719de2" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueNewIssues_cb642cfb-a5cd-4b41-af1b-075720fd8909" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_88c660b4-056e-4cc7-95c8-66dcae765f86" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_1ebd677e-4e54-40a4-ac7d-3be416719de2" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_88c660b4-056e-4cc7-95c8-66dcae765f86" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockOwnershipPlan_00cf4a4f-ce18-45d8-a0e2-0ab44005e2f5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesEmployeeStockOwnershipPlan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_1ebd677e-4e54-40a4-ac7d-3be416719de2" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockOwnershipPlan_00cf4a4f-ce18-45d8-a0e2-0ab44005e2f5" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation_9acead7c-a1ed-4387-b6b9-43eadc8b8105" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_1ebd677e-4e54-40a4-ac7d-3be416719de2" xlink:to="loc_us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation_9acead7c-a1ed-4387-b6b9-43eadc8b8105" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityOther_6f554b63-9653-417e-bf78-22b0f8b1efb2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquityOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_1ebd677e-4e54-40a4-ac7d-3be416719de2" xlink:to="loc_us-gaap_StockholdersEquityOther_6f554b63-9653-417e-bf78-22b0f8b1efb2" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_a009bd57-5981-4e3a-9ba3-9dcbd1fd6044" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_df2bd005-ee81-4f8f-9bf3-caa017015a8a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquity"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fortrea.com/role/SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESNarrativeDetails" xlink:type="simple" xlink:href="ftre-20251231.xsd#SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.fortrea.com/role/SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostLineItems_019c3ff0-38bd-77bc-9cbf-7ffedc2c2406" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CapitalizedContractCostLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostTable_019c3ff0-38bd-7f48-87cf-d5caec6ca9b4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CapitalizedContractCostTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_CapitalizedContractCostLineItems_019c3ff0-38bd-77bc-9cbf-7ffedc2c2406" xlink:to="loc_us-gaap_CapitalizedContractCostTable_019c3ff0-38bd-7f48-87cf-d5caec6ca9b4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019c3ff0-38bd-7ed8-b1ab-bc7d9e743192" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_CapitalizedContractCostTable_019c3ff0-38bd-7f48-87cf-d5caec6ca9b4" xlink:to="loc_srt_RangeAxis_019c3ff0-38bd-7ed8-b1ab-bc7d9e743192" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019c3ff0-38bd-7ed8-b1ab-bc7d9e743192_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019c3ff0-38bd-7ed8-b1ab-bc7d9e743192" xlink:to="loc_srt_RangeMember_019c3ff0-38bd-7ed8-b1ab-bc7d9e743192_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019c3ff0-38bd-7c72-9874-a10e640c2019" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019c3ff0-38bd-7ed8-b1ab-bc7d9e743192" xlink:to="loc_srt_RangeMember_019c3ff0-38bd-7c72-9874-a10e640c2019" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019c3ff0-38bd-7a20-97d7-ffcb750cc4a0" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019c3ff0-38bd-7c72-9874-a10e640c2019" xlink:to="loc_srt_MinimumMember_019c3ff0-38bd-7a20-97d7-ffcb750cc4a0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019c3ff0-38bd-7915-98e7-b9e58a801ef8" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019c3ff0-38bd-7c72-9874-a10e640c2019" xlink:to="loc_srt_MaximumMember_019c3ff0-38bd-7915-98e7-b9e58a801ef8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostAxis_019c3ff0-38bd-740f-90db-6a27695694e2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CapitalizedContractCostAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_CapitalizedContractCostTable_019c3ff0-38bd-7f48-87cf-d5caec6ca9b4" xlink:to="loc_us-gaap_CapitalizedContractCostAxis_019c3ff0-38bd-740f-90db-6a27695694e2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostDomain_019c3ff0-38bd-740f-90db-6a27695694e2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CapitalizedContractCostDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CapitalizedContractCostAxis_019c3ff0-38bd-740f-90db-6a27695694e2" xlink:to="loc_us-gaap_CapitalizedContractCostDomain_019c3ff0-38bd-740f-90db-6a27695694e2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostDomain_019c3ff0-38bd-7c3a-b52c-1c802ec3850d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CapitalizedContractCostDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CapitalizedContractCostAxis_019c3ff0-38bd-740f-90db-6a27695694e2" xlink:to="loc_us-gaap_CapitalizedContractCostDomain_019c3ff0-38bd-7c3a-b52c-1c802ec3850d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_SalesCommissionAssetsMember_019c3ff0-38bd-71b7-b561-5d8b2f7aee8e" xlink:href="ftre-20251231.xsd#ftre_SalesCommissionAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostDomain_019c3ff0-38bd-7c3a-b52c-1c802ec3850d" xlink:to="loc_ftre_SalesCommissionAssetsMember_019c3ff0-38bd-71b7-b561-5d8b2f7aee8e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_DeferredContractCostsMember_019c3ff0-38bd-7149-b7ab-224d296170f5" xlink:href="ftre-20251231.xsd#ftre_DeferredContractCostsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostDomain_019c3ff0-38bd-7c3a-b52c-1c802ec3850d" xlink:to="loc_ftre_DeferredContractCostsMember_019c3ff0-38bd-7149-b7ab-224d296170f5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_019c3ff0-6c7d-7f99-b1bf-c81918b76464" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MajorCustomersAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_CapitalizedContractCostTable_019c3ff0-38bd-7f48-87cf-d5caec6ca9b4" xlink:to="loc_srt_MajorCustomersAxis_019c3ff0-6c7d-7f99-b1bf-c81918b76464" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_019c3ff0-6c7d-7f99-b1bf-c81918b76464_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_019c3ff0-6c7d-7f99-b1bf-c81918b76464" xlink:to="loc_srt_NameOfMajorCustomerDomain_019c3ff0-6c7d-7f99-b1bf-c81918b76464_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_019c3ff0-6c7d-79bc-a84c-542e34fa56e5" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_019c3ff0-6c7d-7f99-b1bf-c81918b76464" xlink:to="loc_srt_NameOfMajorCustomerDomain_019c3ff0-6c7d-79bc-a84c-542e34fa56e5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_CustomerOneMember_019c3ff0-6c7d-7aef-9dfa-5f25e9de5d51" xlink:href="ftre-20251231.xsd#ftre_CustomerOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_019c3ff0-6c7d-79bc-a84c-542e34fa56e5" xlink:to="loc_ftre_CustomerOneMember_019c3ff0-6c7d-7aef-9dfa-5f25e9de5d51" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_PharmaceuticalCustomerOneMember_019c3ff0-6c7d-74b2-afe9-e7325647ce6b" xlink:href="ftre-20251231.xsd#ftre_PharmaceuticalCustomerOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_019c3ff0-6c7d-79bc-a84c-542e34fa56e5" xlink:to="loc_ftre_PharmaceuticalCustomerOneMember_019c3ff0-6c7d-74b2-afe9-e7325647ce6b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_PharmaceuticalCustomerTwoMember_019c3ff0-6c7d-78dc-be52-291532798f6e" xlink:href="ftre-20251231.xsd#ftre_PharmaceuticalCustomerTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_019c3ff0-6c7d-79bc-a84c-542e34fa56e5" xlink:to="loc_ftre_PharmaceuticalCustomerTwoMember_019c3ff0-6c7d-78dc-be52-291532798f6e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_CustomerTwoMember_019c3ff0-6c7d-75ad-9da2-a330872e599e" xlink:href="ftre-20251231.xsd#ftre_CustomerTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_019c3ff0-6c7d-79bc-a84c-542e34fa56e5" xlink:to="loc_ftre_CustomerTwoMember_019c3ff0-6c7d-75ad-9da2-a330872e599e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019c3ff0-6c7d-7e50-a9c9-808bf1df46d7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_CapitalizedContractCostTable_019c3ff0-38bd-7f48-87cf-d5caec6ca9b4" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019c3ff0-6c7d-7e50-a9c9-808bf1df46d7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019c3ff0-6c7d-7e50-a9c9-808bf1df46d7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019c3ff0-6c7d-7e50-a9c9-808bf1df46d7" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019c3ff0-6c7d-7e50-a9c9-808bf1df46d7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019c3ff0-6c7d-7b8e-bf5a-dfae5fa8bd96" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019c3ff0-6c7d-7e50-a9c9-808bf1df46d7" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019c3ff0-6c7d-7b8e-bf5a-dfae5fa8bd96" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableMember_019c3ff0-6c7d-714a-8386-abce93bea6f5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccountsReceivableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019c3ff0-6c7d-7b8e-bf5a-dfae5fa8bd96" xlink:to="loc_us-gaap_AccountsReceivableMember_019c3ff0-6c7d-714a-8386-abce93bea6f5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SalesRevenueNetMember_019c3ff0-6c7d-7bb5-8374-a24cc249e392" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SalesRevenueNetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019c3ff0-6c7d-7b8e-bf5a-dfae5fa8bd96" xlink:to="loc_us-gaap_SalesRevenueNetMember_019c3ff0-6c7d-7bb5-8374-a24cc249e392" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_019c3ff0-6c7d-79e0-aa10-cadf1a10f447" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_CapitalizedContractCostTable_019c3ff0-38bd-7f48-87cf-d5caec6ca9b4" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_019c3ff0-6c7d-79e0-aa10-cadf1a10f447" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019c3ff0-6c7d-79e0-aa10-cadf1a10f447_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019c3ff0-6c7d-79e0-aa10-cadf1a10f447" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019c3ff0-6c7d-79e0-aa10-cadf1a10f447_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019c3ff0-6c7d-7791-aeab-25924ea0e55f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019c3ff0-6c7d-79e0-aa10-cadf1a10f447" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019c3ff0-6c7d-7791-aeab-25924ea0e55f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_019c3ff0-6c7d-7b25-bf5b-2d7d1db2f639" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CustomerConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_019c3ff0-6c7d-7791-aeab-25924ea0e55f" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_019c3ff0-6c7d-7b25-bf5b-2d7d1db2f639" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019c3ff0-9b8d-7977-af74-1493cb16fc7c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_CapitalizedContractCostTable_019c3ff0-38bd-7f48-87cf-d5caec6ca9b4" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019c3ff0-9b8d-7977-af74-1493cb16fc7c" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019c3ff0-9b8d-7977-af74-1493cb16fc7c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019c3ff0-9b8d-7977-af74-1493cb16fc7c" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019c3ff0-9b8d-7977-af74-1493cb16fc7c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019c3ff0-9b8d-7307-8bff-1a400a6aef54" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019c3ff0-9b8d-7977-af74-1493cb16fc7c" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019c3ff0-9b8d-7307-8bff-1a400a6aef54" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SoftwareAndSoftwareDevelopmentCostsMember_019c3ff0-9b8d-751a-a2ca-5e9e6f1f7a89" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SoftwareAndSoftwareDevelopmentCostsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019c3ff0-9b8d-7307-8bff-1a400a6aef54" xlink:to="loc_us-gaap_SoftwareAndSoftwareDevelopmentCostsMember_019c3ff0-9b8d-751a-a2ca-5e9e6f1f7a89" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostAmortizationPeriod_019c3ff0-38bd-7f72-a78a-d160ae7d6545" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CapitalizedContractCostAmortizationPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostLineItems_019c3ff0-38bd-77bc-9cbf-7ffedc2c2406" xlink:to="loc_us-gaap_CapitalizedContractCostAmortizationPeriod_019c3ff0-38bd-7f72-a78a-d160ae7d6545" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_019c3ff0-6c7d-7b06-b799-477a55a745aa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostLineItems_019c3ff0-38bd-77bc-9cbf-7ffedc2c2406" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_019c3ff0-6c7d-7b06-b799-477a55a745aa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_019c3ff0-9b8d-7e63-bb86-319bc759b4a9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostLineItems_019c3ff0-38bd-77bc-9cbf-7ffedc2c2406" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_019c3ff0-9b8d-7e63-bb86-319bc759b4a9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_CapitalizedComputerSoftwareCurrent_019c3ff0-9b8d-754d-97cf-5ac578b3856e" xlink:href="ftre-20251231.xsd#ftre_CapitalizedComputerSoftwareCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostLineItems_019c3ff0-38bd-77bc-9cbf-7ffedc2c2406" xlink:to="loc_ftre_CapitalizedComputerSoftwareCurrent_019c3ff0-9b8d-754d-97cf-5ac578b3856e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_CapitalizedComputerSoftwareNoncurrent_019c3ff0-9b8d-7592-ba84-0bb9378c642c" xlink:href="ftre-20251231.xsd#ftre_CapitalizedComputerSoftwareNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostLineItems_019c3ff0-38bd-77bc-9cbf-7ffedc2c2406" xlink:to="loc_ftre_CapitalizedComputerSoftwareNoncurrent_019c3ff0-9b8d-7592-ba84-0bb9378c642c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_CapitalizedComputerSoftwareExpense_019c7151-4665-7717-9ace-97bfc1ecd744" xlink:href="ftre-20251231.xsd#ftre_CapitalizedComputerSoftwareExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostLineItems_019c3ff0-38bd-77bc-9cbf-7ffedc2c2406" xlink:to="loc_ftre_CapitalizedComputerSoftwareExpense_019c7151-4665-7717-9ace-97bfc1ecd744" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fortrea.com/role/SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESScheduleofPropertyPlantandEquipmentDetails" xlink:type="simple" xlink:href="ftre-20251231.xsd#SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESScheduleofPropertyPlantandEquipmentDetails"/>
  <link:definitionLink xlink:role="http://www.fortrea.com/role/SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESScheduleofPropertyPlantandEquipmentDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_f53ca9f6-52ba-4a75-92be-6e92f6bde0df" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_16cd8a29-7f21-4116-ba1b-40af2ea69227" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_f53ca9f6-52ba-4a75-92be-6e92f6bde0df" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_16cd8a29-7f21-4116-ba1b-40af2ea69227" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_b1fafab3-8e69-43ff-9305-e23a16210f6d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_16cd8a29-7f21-4116-ba1b-40af2ea69227" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_b1fafab3-8e69-43ff-9305-e23a16210f6d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_b1fafab3-8e69-43ff-9305-e23a16210f6d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_b1fafab3-8e69-43ff-9305-e23a16210f6d" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_b1fafab3-8e69-43ff-9305-e23a16210f6d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_f62f7497-b6cb-40f9-8ace-73c329b4a555" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_b1fafab3-8e69-43ff-9305-e23a16210f6d" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_f62f7497-b6cb-40f9-8ace-73c329b4a555" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BuildingAndBuildingImprovementsMember_26170b33-7adb-4286-830a-127d668962d6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BuildingAndBuildingImprovementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_f62f7497-b6cb-40f9-8ace-73c329b4a555" xlink:to="loc_us-gaap_BuildingAndBuildingImprovementsMember_26170b33-7adb-4286-830a-127d668962d6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MachineryAndEquipmentMember_b471ca35-2cd9-42d3-bbbb-5e9abb9c904e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MachineryAndEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_f62f7497-b6cb-40f9-8ace-73c329b4a555" xlink:to="loc_us-gaap_MachineryAndEquipmentMember_b471ca35-2cd9-42d3-bbbb-5e9abb9c904e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FurnitureAndFixturesMember_d497a9a4-879c-49e1-b165-84ee804fe70f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FurnitureAndFixturesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_f62f7497-b6cb-40f9-8ace-73c329b4a555" xlink:to="loc_us-gaap_FurnitureAndFixturesMember_d497a9a4-879c-49e1-b165-84ee804fe70f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SoftwareAndSoftwareDevelopmentCostsMember_406c2eac-0330-408e-bb76-490b9a15f248" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SoftwareAndSoftwareDevelopmentCostsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_f62f7497-b6cb-40f9-8ace-73c329b4a555" xlink:to="loc_us-gaap_SoftwareAndSoftwareDevelopmentCostsMember_406c2eac-0330-408e-bb76-490b9a15f248" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_e79af3ba-bb13-4416-b840-8b3b73fa3507" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_16cd8a29-7f21-4116-ba1b-40af2ea69227" xlink:to="loc_srt_RangeAxis_e79af3ba-bb13-4416-b840-8b3b73fa3507" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_e79af3ba-bb13-4416-b840-8b3b73fa3507_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_e79af3ba-bb13-4416-b840-8b3b73fa3507" xlink:to="loc_srt_RangeMember_e79af3ba-bb13-4416-b840-8b3b73fa3507_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_2c816ece-6b99-4a56-bffc-77ca4c5c9dbf" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_e79af3ba-bb13-4416-b840-8b3b73fa3507" xlink:to="loc_srt_RangeMember_2c816ece-6b99-4a56-bffc-77ca4c5c9dbf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_96cfde01-3569-4a31-96d9-49f7b48dee94" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_2c816ece-6b99-4a56-bffc-77ca4c5c9dbf" xlink:to="loc_srt_MinimumMember_96cfde01-3569-4a31-96d9-49f7b48dee94" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_5251bb6f-c568-48cf-8865-2dc29bc908b7" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_2c816ece-6b99-4a56-bffc-77ca4c5c9dbf" xlink:to="loc_srt_MaximumMember_5251bb6f-c568-48cf-8865-2dc29bc908b7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_6dc3ece4-319c-49aa-ab3f-fcc4663f57ca" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_f53ca9f6-52ba-4a75-92be-6e92f6bde0df" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_6dc3ece4-319c-49aa-ab3f-fcc4663f57ca" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fortrea.com/role/SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESScheduleofIntangibleAssetsDetails" xlink:type="simple" xlink:href="ftre-20251231.xsd#SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESScheduleofIntangibleAssetsDetails"/>
  <link:definitionLink xlink:role="http://www.fortrea.com/role/SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESScheduleofIntangibleAssetsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_12ad0ed8-1f02-45a5-a719-77cce1cd9ebd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_0481df80-6e18-40c9-a8d2-e17cbdec65cc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_12ad0ed8-1f02-45a5-a719-77cce1cd9ebd" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_0481df80-6e18-40c9-a8d2-e17cbdec65cc" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_59edbcc3-74bb-4439-87a2-817612023e0b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_0481df80-6e18-40c9-a8d2-e17cbdec65cc" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_59edbcc3-74bb-4439-87a2-817612023e0b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_59edbcc3-74bb-4439-87a2-817612023e0b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_59edbcc3-74bb-4439-87a2-817612023e0b" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_59edbcc3-74bb-4439-87a2-817612023e0b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_36e591fb-7265-4781-b31b-24f6d4900b43" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_59edbcc3-74bb-4439-87a2-817612023e0b" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_36e591fb-7265-4781-b31b-24f6d4900b43" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_143be99d-66b4-4d3e-adad-52de28eaa95d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_36e591fb-7265-4781-b31b-24f6d4900b43" xlink:to="loc_us-gaap_CustomerRelationshipsMember_143be99d-66b4-4d3e-adad-52de28eaa95d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TechnologyBasedIntangibleAssetsMember_c7d8b47e-b078-4adf-8dd6-1d92662f0a55" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TechnologyBasedIntangibleAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_36e591fb-7265-4781-b31b-24f6d4900b43" xlink:to="loc_us-gaap_TechnologyBasedIntangibleAssetsMember_c7d8b47e-b078-4adf-8dd6-1d92662f0a55" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NoncompeteAgreementsMember_019c119c-c3ee-7244-9a4a-a8f3c8614552" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NoncompeteAgreementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_36e591fb-7265-4781-b31b-24f6d4900b43" xlink:to="loc_us-gaap_NoncompeteAgreementsMember_019c119c-c3ee-7244-9a4a-a8f3c8614552" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_4d0bdc7a-30d0-4f1d-be3e-00756a010347" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_0481df80-6e18-40c9-a8d2-e17cbdec65cc" xlink:to="loc_srt_RangeAxis_4d0bdc7a-30d0-4f1d-be3e-00756a010347" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_4d0bdc7a-30d0-4f1d-be3e-00756a010347_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_4d0bdc7a-30d0-4f1d-be3e-00756a010347" xlink:to="loc_srt_RangeMember_4d0bdc7a-30d0-4f1d-be3e-00756a010347_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_1d2994a3-e01b-480a-8d5a-265c9066ad8a" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_4d0bdc7a-30d0-4f1d-be3e-00756a010347" xlink:to="loc_srt_RangeMember_1d2994a3-e01b-480a-8d5a-265c9066ad8a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_05e59939-089d-40e4-bae9-15397cf8888b" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_1d2994a3-e01b-480a-8d5a-265c9066ad8a" xlink:to="loc_srt_MinimumMember_05e59939-089d-40e4-bae9-15397cf8888b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_cd16beb4-3ebe-40f3-bdb7-bb1412d3a38d" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_1d2994a3-e01b-480a-8d5a-265c9066ad8a" xlink:to="loc_srt_MaximumMember_cd16beb4-3ebe-40f3-bdb7-bb1412d3a38d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_e3140fd4-68c8-4631-80e7-798d0492f46f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_12ad0ed8-1f02-45a5-a719-77cce1cd9ebd" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetUsefulLife_e3140fd4-68c8-4631-80e7-798d0492f46f" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fortrea.com/role/DISCONTINUEDOPERATIONSNarrativeDetails" xlink:type="simple" xlink:href="ftre-20251231.xsd#DISCONTINUEDOPERATIONSNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.fortrea.com/role/DISCONTINUEDOPERATIONSNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_633ee5e7-8aea-44bb-9412-2b7e74557e28" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_8ae65c04-0bf5-49e3-a18e-8f337096405d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_633ee5e7-8aea-44bb-9412-2b7e74557e28" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_8ae65c04-0bf5-49e3-a18e-8f337096405d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_c0c8744f-63ae-4aa5-a459-fa01416504ee" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_8ae65c04-0bf5-49e3-a18e-8f337096405d" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_c0c8744f-63ae-4aa5-a459-fa01416504ee" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_c0c8744f-63ae-4aa5-a459-fa01416504ee_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_c0c8744f-63ae-4aa5-a459-fa01416504ee" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_c0c8744f-63ae-4aa5-a459-fa01416504ee_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_e016bd46-ff5c-4b98-8597-645de293073a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_c0c8744f-63ae-4aa5-a459-fa01416504ee" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_e016bd46-ff5c-4b98-8597-645de293073a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationsDisposedOfBySaleMember_3624a4cb-29d0-441a-870d-d4b8cb7c8638" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DiscontinuedOperationsDisposedOfBySaleMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupClassificationDomain_e016bd46-ff5c-4b98-8597-645de293073a" xlink:to="loc_us-gaap_DiscontinuedOperationsDisposedOfBySaleMember_3624a4cb-29d0-441a-870d-d4b8cb7c8638" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_1dc8e7d9-b00d-4670-968d-cea090e65b73" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_8ae65c04-0bf5-49e3-a18e-8f337096405d" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_1dc8e7d9-b00d-4670-968d-cea090e65b73" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_1dc8e7d9-b00d-4670-968d-cea090e65b73_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_1dc8e7d9-b00d-4670-968d-cea090e65b73" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_1dc8e7d9-b00d-4670-968d-cea090e65b73_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_050d3dcb-941e-4071-bf9a-803d629f3116" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_1dc8e7d9-b00d-4670-968d-cea090e65b73" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_050d3dcb-941e-4071-bf9a-803d629f3116" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_EnablingServicesSegmentDisposalMember_6c1e3077-5646-4f2c-8947-24f3c3404da1" xlink:href="ftre-20251231.xsd#ftre_EnablingServicesSegmentDisposalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_050d3dcb-941e-4071-bf9a-803d629f3116" xlink:to="loc_ftre_EnablingServicesSegmentDisposalMember_6c1e3077-5646-4f2c-8947-24f3c3404da1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019b2ca9-e1e9-73a7-9e02-95c3c12e0ceb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_8ae65c04-0bf5-49e3-a18e-8f337096405d" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019b2ca9-e1e9-73a7-9e02-95c3c12e0ceb" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019b2ca9-e1e9-73a7-9e02-95c3c12e0ceb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019b2ca9-e1e9-73a7-9e02-95c3c12e0ceb" xlink:to="loc_us-gaap_SegmentDomain_019b2ca9-e1e9-73a7-9e02-95c3c12e0ceb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019b2ca9-e1e9-731f-858a-74ec494c7e6a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019b2ca9-e1e9-73a7-9e02-95c3c12e0ceb" xlink:to="loc_us-gaap_SegmentDomain_019b2ca9-e1e9-731f-858a-74ec494c7e6a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_EnablingServicesSegmentMember_019b2caa-12f5-756f-a5e7-5b772ab9af80" xlink:href="ftre-20251231.xsd#ftre_EnablingServicesSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019b2ca9-e1e9-731f-858a-74ec494c7e6a" xlink:to="loc_ftre_EnablingServicesSegmentMember_019b2caa-12f5-756f-a5e7-5b772ab9af80" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration_f04d37de-e822-4594-a435-7369d52a98a0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_633ee5e7-8aea-44bb-9412-2b7e74557e28" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationConsideration_f04d37de-e822-4594-a435-7369d52a98a0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_DisposalGroupIncludingDiscontinuedOperationConsiderationCash_58b2d054-d275-435a-a02f-ac9581b466c4" xlink:href="ftre-20251231.xsd#ftre_DisposalGroupIncludingDiscontinuedOperationConsiderationCash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_633ee5e7-8aea-44bb-9412-2b7e74557e28" xlink:to="loc_ftre_DisposalGroupIncludingDiscontinuedOperationConsiderationCash_58b2d054-d275-435a-a02f-ac9581b466c4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_DisposalGroupIncludingDiscontinuedOperationConsiderationLiability_bcaf0de1-2e83-415f-88c7-b09d0b044285" xlink:href="ftre-20251231.xsd#ftre_DisposalGroupIncludingDiscontinuedOperationConsiderationLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_633ee5e7-8aea-44bb-9412-2b7e74557e28" xlink:to="loc_ftre_DisposalGroupIncludingDiscontinuedOperationConsiderationLiability_bcaf0de1-2e83-415f-88c7-b09d0b044285" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_DisposalGroupIncludingDiscontinuedOperationMilestoneClosingPaymentReceived_a29150fe-0e32-402c-8b19-48b724b77009" xlink:href="ftre-20251231.xsd#ftre_DisposalGroupIncludingDiscontinuedOperationMilestoneClosingPaymentReceived"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_633ee5e7-8aea-44bb-9412-2b7e74557e28" xlink:to="loc_ftre_DisposalGroupIncludingDiscontinuedOperationMilestoneClosingPaymentReceived_a29150fe-0e32-402c-8b19-48b724b77009" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax_7c25bdd2-5631-4b0e-9cc8-5608f34b1b19" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_633ee5e7-8aea-44bb-9412-2b7e74557e28" xlink:to="loc_us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax_7c25bdd2-5631-4b0e-9cc8-5608f34b1b19" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillImpairmentLossStatementOfIncomeOrComprehensiveIncomeExtensibleEnumeration_48be7b9c-1a13-4268-a174-958db89b5a9b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GoodwillImpairmentLossStatementOfIncomeOrComprehensiveIncomeExtensibleEnumeration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_633ee5e7-8aea-44bb-9412-2b7e74557e28" xlink:to="loc_us-gaap_GoodwillImpairmentLossStatementOfIncomeOrComprehensiveIncomeExtensibleEnumeration_48be7b9c-1a13-4268-a174-958db89b5a9b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillImpairmentLoss_53ea0525-b44b-46a6-a82f-95155df1b085" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GoodwillImpairmentLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_633ee5e7-8aea-44bb-9412-2b7e74557e28" xlink:to="loc_us-gaap_GoodwillImpairmentLoss_53ea0525-b44b-46a6-a82f-95155df1b085" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fortrea.com/role/DISCONTINUEDOPERATIONSEarningsfromDiscontinuedOperationsDetails" xlink:type="simple" xlink:href="ftre-20251231.xsd#DISCONTINUEDOPERATIONSEarningsfromDiscontinuedOperationsDetails"/>
  <link:definitionLink xlink:role="http://www.fortrea.com/role/DISCONTINUEDOPERATIONSEarningsfromDiscontinuedOperationsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_b85fe88f-b60f-4730-b446-9cb09636a4e8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_1c62c6f1-54a9-4fad-9a29-d359699dfde2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_b85fe88f-b60f-4730-b446-9cb09636a4e8" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_1c62c6f1-54a9-4fad-9a29-d359699dfde2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_a0a4afc4-d29c-45d8-a1b7-1254bb2245cc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_1c62c6f1-54a9-4fad-9a29-d359699dfde2" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_a0a4afc4-d29c-45d8-a1b7-1254bb2245cc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_a0a4afc4-d29c-45d8-a1b7-1254bb2245cc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_a0a4afc4-d29c-45d8-a1b7-1254bb2245cc" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_a0a4afc4-d29c-45d8-a1b7-1254bb2245cc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_c4b9d6fd-e184-4f6a-9179-b145bb796c05" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_a0a4afc4-d29c-45d8-a1b7-1254bb2245cc" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_c4b9d6fd-e184-4f6a-9179-b145bb796c05" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationsDisposedOfBySaleMember_8de644cd-2953-442b-abc1-b9379ba2ad8e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DiscontinuedOperationsDisposedOfBySaleMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupClassificationDomain_c4b9d6fd-e184-4f6a-9179-b145bb796c05" xlink:to="loc_us-gaap_DiscontinuedOperationsDisposedOfBySaleMember_8de644cd-2953-442b-abc1-b9379ba2ad8e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_7625714e-3eb8-4275-97c8-03a24879478c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_1c62c6f1-54a9-4fad-9a29-d359699dfde2" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_7625714e-3eb8-4275-97c8-03a24879478c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_7625714e-3eb8-4275-97c8-03a24879478c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_7625714e-3eb8-4275-97c8-03a24879478c" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_7625714e-3eb8-4275-97c8-03a24879478c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_11c98514-310c-44f6-a557-ebde5d635be1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_7625714e-3eb8-4275-97c8-03a24879478c" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_11c98514-310c-44f6-a557-ebde5d635be1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_EnablingServicesSegmentDisposalMember_d7af8ac7-16d4-4628-933a-edcf502a43fa" xlink:href="ftre-20251231.xsd#ftre_EnablingServicesSegmentDisposalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_11c98514-310c-44f6-a557-ebde5d635be1" xlink:to="loc_ftre_EnablingServicesSegmentDisposalMember_d7af8ac7-16d4-4628-933a-edcf502a43fa" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationRevenue_f1c15f79-d302-4b38-8767-4a7205e975e6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_b85fe88f-b60f-4730-b446-9cb09636a4e8" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationRevenue_f1c15f79-d302-4b38-8767-4a7205e975e6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_DisposalGroupNotDiscontinuedOperationCostsAndExpensesAbstract_f35e583c-c25e-42be-83fd-02a482a8fa6e" xlink:href="ftre-20251231.xsd#ftre_DisposalGroupNotDiscontinuedOperationCostsAndExpensesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_b85fe88f-b60f-4730-b446-9cb09636a4e8" xlink:to="loc_ftre_DisposalGroupNotDiscontinuedOperationCostsAndExpensesAbstract_f35e583c-c25e-42be-83fd-02a482a8fa6e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationCostsOfGoodsSold_d4f47d4e-4f10-4f2a-9b2c-92dcded2fee2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationCostsOfGoodsSold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ftre_DisposalGroupNotDiscontinuedOperationCostsAndExpensesAbstract_f35e583c-c25e-42be-83fd-02a482a8fa6e" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationCostsOfGoodsSold_d4f47d4e-4f10-4f2a-9b2c-92dcded2fee2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationGeneralAndAdministrativeExpense_fbfca6c5-f81c-4fff-a1e8-93ba737af827" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationGeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ftre_DisposalGroupNotDiscontinuedOperationCostsAndExpensesAbstract_f35e583c-c25e-42be-83fd-02a482a8fa6e" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationGeneralAndAdministrativeExpense_fbfca6c5-f81c-4fff-a1e8-93ba737af827" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationDepreciationAndAmortization_5a033143-2c85-4a99-9dbe-bfa5f16fe081" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationDepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ftre_DisposalGroupNotDiscontinuedOperationCostsAndExpensesAbstract_f35e583c-c25e-42be-83fd-02a482a8fa6e" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationDepreciationAndAmortization_5a033143-2c85-4a99-9dbe-bfa5f16fe081" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_DisposalGroupIncludingDiscontinuedOperationAssetImpairmentCharges_c40e4a1e-5eb1-4c4d-b5d1-2dd9ea74e4bc" xlink:href="ftre-20251231.xsd#ftre_DisposalGroupIncludingDiscontinuedOperationAssetImpairmentCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ftre_DisposalGroupNotDiscontinuedOperationCostsAndExpensesAbstract_f35e583c-c25e-42be-83fd-02a482a8fa6e" xlink:to="loc_ftre_DisposalGroupIncludingDiscontinuedOperationAssetImpairmentCharges_c40e4a1e-5eb1-4c4d-b5d1-2dd9ea74e4bc" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_DisposalGroupIncludingDiscontinuedOperationRestructuringAndOtherCharges_ab649966-4378-4c19-b49a-e54a93c9ed09" xlink:href="ftre-20251231.xsd#ftre_DisposalGroupIncludingDiscontinuedOperationRestructuringAndOtherCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ftre_DisposalGroupNotDiscontinuedOperationCostsAndExpensesAbstract_f35e583c-c25e-42be-83fd-02a482a8fa6e" xlink:to="loc_ftre_DisposalGroupIncludingDiscontinuedOperationRestructuringAndOtherCharges_ab649966-4378-4c19-b49a-e54a93c9ed09" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_DisposalGroupIncludingDiscontinuedOperationCostsAndExpense_7e96f927-77cf-4942-b46a-aff4060e6a9a" xlink:href="ftre-20251231.xsd#ftre_DisposalGroupIncludingDiscontinuedOperationCostsAndExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ftre_DisposalGroupNotDiscontinuedOperationCostsAndExpensesAbstract_f35e583c-c25e-42be-83fd-02a482a8fa6e" xlink:to="loc_ftre_DisposalGroupIncludingDiscontinuedOperationCostsAndExpense_7e96f927-77cf-4942-b46a-aff4060e6a9a" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationOperatingIncomeLoss_802a2847-f9dc-438a-8567-33ea1fe23dc6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationOperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_b85fe88f-b60f-4730-b446-9cb09636a4e8" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationOperatingIncomeLoss_802a2847-f9dc-438a-8567-33ea1fe23dc6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_DisposalGroupIncludingDiscontinuedOperationOtherIncomeExpenseAbstract_c0fafb5a-bc23-409d-b5a1-a6099960cb3e" xlink:href="ftre-20251231.xsd#ftre_DisposalGroupIncludingDiscontinuedOperationOtherIncomeExpenseAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_b85fe88f-b60f-4730-b446-9cb09636a4e8" xlink:to="loc_ftre_DisposalGroupIncludingDiscontinuedOperationOtherIncomeExpenseAbstract_c0fafb5a-bc23-409d-b5a1-a6099960cb3e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_DisposalGroupIncludingDiscontinuedOperationGainLossForeignCurrencyTransaction_140f8b96-a8cb-4ab2-9a9a-52c5cc280952" xlink:href="ftre-20251231.xsd#ftre_DisposalGroupIncludingDiscontinuedOperationGainLossForeignCurrencyTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ftre_DisposalGroupIncludingDiscontinuedOperationOtherIncomeExpenseAbstract_c0fafb5a-bc23-409d-b5a1-a6099960cb3e" xlink:to="loc_ftre_DisposalGroupIncludingDiscontinuedOperationGainLossForeignCurrencyTransaction_140f8b96-a8cb-4ab2-9a9a-52c5cc280952" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationGainLossFromDisposalOfDiscontinuedOperationBeforeIncomeTax_bde9bc53-97e8-42b3-813a-b16b4ffea5f6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DiscontinuedOperationGainLossFromDisposalOfDiscontinuedOperationBeforeIncomeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ftre_DisposalGroupIncludingDiscontinuedOperationOtherIncomeExpenseAbstract_c0fafb5a-bc23-409d-b5a1-a6099960cb3e" xlink:to="loc_us-gaap_DiscontinuedOperationGainLossFromDisposalOfDiscontinuedOperationBeforeIncomeTax_bde9bc53-97e8-42b3-813a-b16b4ffea5f6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_DisposalGroupIncludingDiscontinuedOperationOtherIncomeExpense_4d6bc634-9962-4a5c-8c7f-0bd45d1cce41" xlink:href="ftre-20251231.xsd#ftre_DisposalGroupIncludingDiscontinuedOperationOtherIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ftre_DisposalGroupIncludingDiscontinuedOperationOtherIncomeExpenseAbstract_c0fafb5a-bc23-409d-b5a1-a6099960cb3e" xlink:to="loc_ftre_DisposalGroupIncludingDiscontinuedOperationOtherIncomeExpense_4d6bc634-9962-4a5c-8c7f-0bd45d1cce41" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationBeforeIncomeTax_ae861a4a-992f-46e4-b465-a9ccf8834d72" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationBeforeIncomeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_b85fe88f-b60f-4730-b446-9cb09636a4e8" xlink:to="loc_us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationBeforeIncomeTax_ae861a4a-992f-46e4-b465-a9ccf8834d72" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationTaxEffectOfDiscontinuedOperation_35190dd5-ff5e-4680-a043-f0dfadc756a8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DiscontinuedOperationTaxEffectOfDiscontinuedOperation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_b85fe88f-b60f-4730-b446-9cb09636a4e8" xlink:to="loc_us-gaap_DiscontinuedOperationTaxEffectOfDiscontinuedOperation_35190dd5-ff5e-4680-a043-f0dfadc756a8" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity_d0d913b2-7f7c-4081-8909-b9e624f410a4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_b85fe88f-b60f-4730-b446-9cb09636a4e8" xlink:to="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity_d0d913b2-7f7c-4081-8909-b9e624f410a4" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationDuringPhaseOutPeriodNetOfTax_cb098ab0-015e-4611-aa93-c58865592897" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationDuringPhaseOutPeriodNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_b85fe88f-b60f-4730-b446-9cb09636a4e8" xlink:to="loc_us-gaap_DiscontinuedOperationIncomeLossFromDiscontinuedOperationDuringPhaseOutPeriodNetOfTax_cb098ab0-015e-4611-aa93-c58865592897" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax_8e6e605a-f94c-4263-bd31-6d66f07573b1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_b85fe88f-b60f-4730-b446-9cb09636a4e8" xlink:to="loc_us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax_8e6e605a-f94c-4263-bd31-6d66f07573b1" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity_f98c9228-55dd-4412-ae6a-dd5aa4d742ee" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fortrea.com/role/DISCONTINUEDOPERATIONSScheduleofSelectedInformationonCashFlowsRelatedtoDiscontinuedOperationsDetails" xlink:type="simple" xlink:href="ftre-20251231.xsd#DISCONTINUEDOPERATIONSScheduleofSelectedInformationonCashFlowsRelatedtoDiscontinuedOperationsDetails"/>
  <link:definitionLink xlink:role="http://www.fortrea.com/role/DISCONTINUEDOPERATIONSScheduleofSelectedInformationonCashFlowsRelatedtoDiscontinuedOperationsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_2a853f07-3224-4c15-ace4-ba3f2a28a566" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_935938f2-fdf4-4d25-a22b-cd4325520598" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_2a853f07-3224-4c15-ace4-ba3f2a28a566" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_935938f2-fdf4-4d25-a22b-cd4325520598" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationAxis_94d64544-104e-4212-adbf-deeca6ce63c2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupClassificationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_935938f2-fdf4-4d25-a22b-cd4325520598" xlink:to="loc_us-gaap_DisposalGroupClassificationAxis_94d64544-104e-4212-adbf-deeca6ce63c2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_94d64544-104e-4212-adbf-deeca6ce63c2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_94d64544-104e-4212-adbf-deeca6ce63c2" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_94d64544-104e-4212-adbf-deeca6ce63c2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupClassificationDomain_8d5a645b-eeb4-431a-8605-285cb2d4e1dd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupClassificationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DisposalGroupClassificationAxis_94d64544-104e-4212-adbf-deeca6ce63c2" xlink:to="loc_us-gaap_DisposalGroupClassificationDomain_8d5a645b-eeb4-431a-8605-285cb2d4e1dd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationsDisposedOfBySaleMember_03f90cb0-81ea-4d36-b09f-743843abed18" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DiscontinuedOperationsDisposedOfBySaleMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupClassificationDomain_8d5a645b-eeb4-431a-8605-285cb2d4e1dd" xlink:to="loc_us-gaap_DiscontinuedOperationsDisposedOfBySaleMember_03f90cb0-81ea-4d36-b09f-743843abed18" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_03533241-ccd5-43e4-a3f9-ac20b5e22dc7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsTable_935938f2-fdf4-4d25-a22b-cd4325520598" xlink:to="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_03533241-ccd5-43e4-a3f9-ac20b5e22dc7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_03533241-ccd5-43e4-a3f9-ac20b5e22dc7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_03533241-ccd5-43e4-a3f9-ac20b5e22dc7" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_03533241-ccd5-43e4-a3f9-ac20b5e22dc7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_bec270fa-77f4-42a6-943e-f939a4044efe" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsAxis_03533241-ccd5-43e4-a3f9-ac20b5e22dc7" xlink:to="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_bec270fa-77f4-42a6-943e-f939a4044efe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_EnablingServicesSegmentDisposalMember_e0a61f68-0e2f-4032-b82e-572de5b78b2b" xlink:href="ftre-20251231.xsd#ftre_EnablingServicesSegmentDisposalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisposalGroupsIncludingDiscontinuedOperationsNameDomain_bec270fa-77f4-42a6-943e-f939a4044efe" xlink:to="loc_ftre_EnablingServicesSegmentDisposalMember_e0a61f68-0e2f-4032-b82e-572de5b78b2b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationDepreciationAndAmortization_9d5b2899-37a5-478d-9da2-851a91476fdb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisposalGroupIncludingDiscontinuedOperationDepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_2a853f07-3224-4c15-ace4-ba3f2a28a566" xlink:to="loc_us-gaap_DisposalGroupIncludingDiscontinuedOperationDepreciationAndAmortization_9d5b2899-37a5-478d-9da2-851a91476fdb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_DisposalGroupIncludingDiscontinuedOperationGoodwillImpairment_e6013a5c-fdca-41e2-8a0d-290d90e8fbb9" xlink:href="ftre-20251231.xsd#ftre_DisposalGroupIncludingDiscontinuedOperationGoodwillImpairment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_2a853f07-3224-4c15-ace4-ba3f2a28a566" xlink:to="loc_ftre_DisposalGroupIncludingDiscontinuedOperationGoodwillImpairment_e6013a5c-fdca-41e2-8a0d-290d90e8fbb9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax_038b483f-f0b7-488e-96ba-86d84eed9d80" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_2a853f07-3224-4c15-ace4-ba3f2a28a566" xlink:to="loc_us-gaap_DiscontinuedOperationGainLossOnDisposalOfDiscontinuedOperationNetOfTax_038b483f-f0b7-488e-96ba-86d84eed9d80" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_DisposalGroupIncludingDiscontinuedOperationCapitalExpenditures_467acb01-571d-49be-b129-43faf431d578" xlink:href="ftre-20251231.xsd#ftre_DisposalGroupIncludingDiscontinuedOperationCapitalExpenditures"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementBalanceSheetAndAdditionalDisclosuresByDisposalGroupsIncludingDiscontinuedOperationsLineItems_2a853f07-3224-4c15-ace4-ba3f2a28a566" xlink:to="loc_ftre_DisposalGroupIncludingDiscontinuedOperationCapitalExpenditures_467acb01-571d-49be-b129-43faf431d578" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fortrea.com/role/REVENUESScheduleofRevenuebySegmentandGeographyDetails" xlink:type="simple" xlink:href="ftre-20251231.xsd#REVENUESScheduleofRevenuebySegmentandGeographyDetails"/>
  <link:definitionLink xlink:role="http://www.fortrea.com/role/REVENUESScheduleofRevenuebySegmentandGeographyDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_85bb715e-f308-4c33-adea-86fb4d00d615" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_1bfa918a-b7b7-44cd-a3b8-966e72f0c9d6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_85bb715e-f308-4c33-adea-86fb4d00d615" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_1bfa918a-b7b7-44cd-a3b8-966e72f0c9d6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_7c9635ee-ccd4-4699-910b-97958c6ec0ca" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_1bfa918a-b7b7-44cd-a3b8-966e72f0c9d6" xlink:to="loc_srt_StatementGeographicalAxis_7c9635ee-ccd4-4699-910b-97958c6ec0ca" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_7c9635ee-ccd4-4699-910b-97958c6ec0ca_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_7c9635ee-ccd4-4699-910b-97958c6ec0ca" xlink:to="loc_srt_SegmentGeographicalDomain_7c9635ee-ccd4-4699-910b-97958c6ec0ca_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_b485d9fd-120f-4885-9e92-f081cc1aa971" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_7c9635ee-ccd4-4699-910b-97958c6ec0ca" xlink:to="loc_srt_SegmentGeographicalDomain_b485d9fd-120f-4885-9e92-f081cc1aa971" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NorthAmericaMember_255507f6-ee00-4cff-8109-d356bf8f44a4" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_NorthAmericaMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_b485d9fd-120f-4885-9e92-f081cc1aa971" xlink:to="loc_srt_NorthAmericaMember_255507f6-ee00-4cff-8109-d356bf8f44a4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EuropeMember_32d50db7-ed8a-4aec-a17f-af8bdd0127a8" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_EuropeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_b485d9fd-120f-4885-9e92-f081cc1aa971" xlink:to="loc_srt_EuropeMember_32d50db7-ed8a-4aec-a17f-af8bdd0127a8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_OtherGeographicalAreasMember_d8e95e17-5751-4e77-864a-a8ef0e739673" xlink:href="ftre-20251231.xsd#ftre_OtherGeographicalAreasMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_b485d9fd-120f-4885-9e92-f081cc1aa971" xlink:to="loc_ftre_OtherGeographicalAreasMember_d8e95e17-5751-4e77-864a-a8ef0e739673" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_b7111b9b-7bd4-4ea8-b664-34a67fc042a6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_85bb715e-f308-4c33-adea-86fb4d00d615" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_b7111b9b-7bd4-4ea8-b664-34a67fc042a6" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fortrea.com/role/REVENUESScheduleofCapitalizedContractCostDetails" xlink:type="simple" xlink:href="ftre-20251231.xsd#REVENUESScheduleofCapitalizedContractCostDetails"/>
  <link:definitionLink xlink:role="http://www.fortrea.com/role/REVENUESScheduleofCapitalizedContractCostDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostLineItems_8b932b58-8632-4c1c-8fd1-856103c59181" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CapitalizedContractCostLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostTable_d56bfd94-8588-408e-8e6e-37861f90dfc9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CapitalizedContractCostTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_CapitalizedContractCostLineItems_8b932b58-8632-4c1c-8fd1-856103c59181" xlink:to="loc_us-gaap_CapitalizedContractCostTable_d56bfd94-8588-408e-8e6e-37861f90dfc9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostAxis_52007b32-7b1e-460b-bb12-23b85eac7e09" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CapitalizedContractCostAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_CapitalizedContractCostTable_d56bfd94-8588-408e-8e6e-37861f90dfc9" xlink:to="loc_us-gaap_CapitalizedContractCostAxis_52007b32-7b1e-460b-bb12-23b85eac7e09" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostDomain_52007b32-7b1e-460b-bb12-23b85eac7e09_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CapitalizedContractCostDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CapitalizedContractCostAxis_52007b32-7b1e-460b-bb12-23b85eac7e09" xlink:to="loc_us-gaap_CapitalizedContractCostDomain_52007b32-7b1e-460b-bb12-23b85eac7e09_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostDomain_7d34db84-b536-4c65-a9a5-e6cce0714aaf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CapitalizedContractCostDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CapitalizedContractCostAxis_52007b32-7b1e-460b-bb12-23b85eac7e09" xlink:to="loc_us-gaap_CapitalizedContractCostDomain_7d34db84-b536-4c65-a9a5-e6cce0714aaf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_SalesCommissionAssetsMember_b0540d62-7810-48cb-8cee-ff5dd9dfbeeb" xlink:href="ftre-20251231.xsd#ftre_SalesCommissionAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostDomain_7d34db84-b536-4c65-a9a5-e6cce0714aaf" xlink:to="loc_ftre_SalesCommissionAssetsMember_b0540d62-7810-48cb-8cee-ff5dd9dfbeeb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_DeferredContractCostsMember_002b2939-ba12-4f1b-a96a-34b98f9c28f6" xlink:href="ftre-20251231.xsd#ftre_DeferredContractCostsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostDomain_7d34db84-b536-4c65-a9a5-e6cce0714aaf" xlink:to="loc_ftre_DeferredContractCostsMember_002b2939-ba12-4f1b-a96a-34b98f9c28f6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostNet_ebd49d60-521e-44a5-a8ef-c91aab4cf848" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CapitalizedContractCostNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostLineItems_8b932b58-8632-4c1c-8fd1-856103c59181" xlink:to="loc_us-gaap_CapitalizedContractCostNet_ebd49d60-521e-44a5-a8ef-c91aab4cf848" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fortrea.com/role/REVENUESNarrativeDetails" xlink:type="simple" xlink:href="ftre-20251231.xsd#REVENUESNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.fortrea.com/role/REVENUESNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostLineItems_35ed13f7-5377-4795-9217-0a535ca85ed7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CapitalizedContractCostLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostTable_8ba39edc-273f-4be8-88e3-6107bd27e38a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CapitalizedContractCostTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_CapitalizedContractCostLineItems_35ed13f7-5377-4795-9217-0a535ca85ed7" xlink:to="loc_us-gaap_CapitalizedContractCostTable_8ba39edc-273f-4be8-88e3-6107bd27e38a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostAxis_239a7c61-cbed-468a-8f6d-02fdec94535b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CapitalizedContractCostAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_CapitalizedContractCostTable_8ba39edc-273f-4be8-88e3-6107bd27e38a" xlink:to="loc_us-gaap_CapitalizedContractCostAxis_239a7c61-cbed-468a-8f6d-02fdec94535b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostDomain_239a7c61-cbed-468a-8f6d-02fdec94535b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CapitalizedContractCostDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CapitalizedContractCostAxis_239a7c61-cbed-468a-8f6d-02fdec94535b" xlink:to="loc_us-gaap_CapitalizedContractCostDomain_239a7c61-cbed-468a-8f6d-02fdec94535b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostDomain_9c200ef7-9d38-479e-b20f-3184c58d45c0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CapitalizedContractCostDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CapitalizedContractCostAxis_239a7c61-cbed-468a-8f6d-02fdec94535b" xlink:to="loc_us-gaap_CapitalizedContractCostDomain_9c200ef7-9d38-479e-b20f-3184c58d45c0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_SalesCommissionAssetsMember_6b693884-0015-405e-b806-30d164e4ca53" xlink:href="ftre-20251231.xsd#ftre_SalesCommissionAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostDomain_9c200ef7-9d38-479e-b20f-3184c58d45c0" xlink:to="loc_ftre_SalesCommissionAssetsMember_6b693884-0015-405e-b806-30d164e4ca53" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_DeferredContractCostsMember_1cef6842-ffcd-41ca-83f3-11da6e8c9417" xlink:href="ftre-20251231.xsd#ftre_DeferredContractCostsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostDomain_9c200ef7-9d38-479e-b20f-3184c58d45c0" xlink:to="loc_ftre_DeferredContractCostsMember_1cef6842-ffcd-41ca-83f3-11da6e8c9417" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_5347d6f4-93a3-4821-90b6-eb383b455fa5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_CapitalizedContractCostTable_8ba39edc-273f-4be8-88e3-6107bd27e38a" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionStartDateAxis_5347d6f4-93a3-4821-90b6-eb383b455fa5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_ba43c065-de2e-4fb1-a242-2de169a6b4ec" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_CapitalizedContractCostTable_8ba39edc-273f-4be8-88e3-6107bd27e38a" xlink:to="loc_srt_RangeAxis_ba43c065-de2e-4fb1-a242-2de169a6b4ec" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_ba43c065-de2e-4fb1-a242-2de169a6b4ec_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_ba43c065-de2e-4fb1-a242-2de169a6b4ec" xlink:to="loc_srt_RangeMember_ba43c065-de2e-4fb1-a242-2de169a6b4ec_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_c4df0200-f767-4709-adcf-fa60f5a906d4" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_ba43c065-de2e-4fb1-a242-2de169a6b4ec" xlink:to="loc_srt_RangeMember_c4df0200-f767-4709-adcf-fa60f5a906d4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_12f711c2-3f5f-445c-8612-15faba1a7983" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_c4df0200-f767-4709-adcf-fa60f5a906d4" xlink:to="loc_srt_MinimumMember_12f711c2-3f5f-445c-8612-15faba1a7983" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_fc6beb4c-39e6-4270-bf06-db671a371a6d" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_c4df0200-f767-4709-adcf-fa60f5a906d4" xlink:to="loc_srt_MaximumMember_fc6beb4c-39e6-4270-bf06-db671a371a6d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ChangeInAccountingEstimateByTypeAxis_c2977487-f7d0-4595-866c-b263ee5af2e7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ChangeInAccountingEstimateByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_CapitalizedContractCostTable_8ba39edc-273f-4be8-88e3-6107bd27e38a" xlink:to="loc_us-gaap_ChangeInAccountingEstimateByTypeAxis_c2977487-f7d0-4595-866c-b263ee5af2e7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ChangeInAccountingEstimateTypeDomain_c2977487-f7d0-4595-866c-b263ee5af2e7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ChangeInAccountingEstimateTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ChangeInAccountingEstimateByTypeAxis_c2977487-f7d0-4595-866c-b263ee5af2e7" xlink:to="loc_us-gaap_ChangeInAccountingEstimateTypeDomain_c2977487-f7d0-4595-866c-b263ee5af2e7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ChangeInAccountingEstimateTypeDomain_05bc745b-7e98-4b48-be32-1459a67b62b9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ChangeInAccountingEstimateTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ChangeInAccountingEstimateByTypeAxis_c2977487-f7d0-4595-866c-b263ee5af2e7" xlink:to="loc_us-gaap_ChangeInAccountingEstimateTypeDomain_05bc745b-7e98-4b48-be32-1459a67b62b9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_ChangeInScopeAndChangeInEstimatedEffortToCompleteContractMember_58944246-5c9f-4aac-9c6f-0acb5bba1892" xlink:href="ftre-20251231.xsd#ftre_ChangeInScopeAndChangeInEstimatedEffortToCompleteContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ChangeInAccountingEstimateTypeDomain_05bc745b-7e98-4b48-be32-1459a67b62b9" xlink:to="loc_ftre_ChangeInScopeAndChangeInEstimatedEffortToCompleteContractMember_58944246-5c9f-4aac-9c6f-0acb5bba1892" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostAmortization_6e6a4161-552a-492b-903d-2351ab6571a6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CapitalizedContractCostAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostLineItems_35ed13f7-5377-4795-9217-0a535ca85ed7" xlink:to="loc_us-gaap_CapitalizedContractCostAmortization_6e6a4161-552a-492b-903d-2351ab6571a6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_2f8d336b-26b3-4f92-a2f5-24a99f724478" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractWithCustomerLiabilityRevenueRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostLineItems_35ed13f7-5377-4795-9217-0a535ca85ed7" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_2f8d336b-26b3-4f92-a2f5-24a99f724478" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableSale_2d7b7ab3-2df8-48cc-9f49-a9547a6f664d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccountsReceivableSale"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostLineItems_35ed13f7-5377-4795-9217-0a535ca85ed7" xlink:to="loc_us-gaap_AccountsReceivableSale_2d7b7ab3-2df8-48cc-9f49-a9547a6f664d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligation_7b41647f-7c7d-40bd-a588-e83a9f5156bc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostLineItems_35ed13f7-5377-4795-9217-0a535ca85ed7" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligation_7b41647f-7c7d-40bd-a588-e83a9f5156bc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_c0e0e5cf-5d86-478e-a7fd-bea218458670" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostLineItems_35ed13f7-5377-4795-9217-0a535ca85ed7" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_c0e0e5cf-5d86-478e-a7fd-bea218458670" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_f8d0b4f6-be29-4e27-9a25-9a0debb4964a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostLineItems_35ed13f7-5377-4795-9217-0a535ca85ed7" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_f8d0b4f6-be29-4e27-9a25-9a0debb4964a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerPerformanceObligationSatisfiedInPreviousPeriod_548f4ff4-09f9-4ea8-9c30-8801fa63c57c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractWithCustomerPerformanceObligationSatisfiedInPreviousPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostLineItems_35ed13f7-5377-4795-9217-0a535ca85ed7" xlink:to="loc_us-gaap_ContractWithCustomerPerformanceObligationSatisfiedInPreviousPeriod_548f4ff4-09f9-4ea8-9c30-8801fa63c57c" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_d8215e29-1eb3-4a16-a3ee-144eee6624cf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostLineItems_35ed13f7-5377-4795-9217-0a535ca85ed7" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_d8215e29-1eb3-4a16-a3ee-144eee6624cf" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_a65653ed-d41a-46ae-875a-2f45d2117190" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostLineItems_35ed13f7-5377-4795-9217-0a535ca85ed7" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_a65653ed-d41a-46ae-875a-2f45d2117190" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasic_3e9a5f0c-de57-42b5-b41e-e20e84809ea2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EarningsPerShareBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostLineItems_35ed13f7-5377-4795-9217-0a535ca85ed7" xlink:to="loc_us-gaap_EarningsPerShareBasic_3e9a5f0c-de57-42b5-b41e-e20e84809ea2" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_AccountsReceivablePurchaseProgramMaximumFacilityAmount_2f40f0d0-52e0-403b-8070-e3f2077b4114" xlink:href="ftre-20251231.xsd#ftre_AccountsReceivablePurchaseProgramMaximumFacilityAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostLineItems_35ed13f7-5377-4795-9217-0a535ca85ed7" xlink:to="loc_ftre_AccountsReceivablePurchaseProgramMaximumFacilityAmount_2f40f0d0-52e0-403b-8070-e3f2077b4114" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromSaleOfOtherReceivables_86060f85-588f-40dd-8189-7d33c150c34a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProceedsFromSaleOfOtherReceivables"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostLineItems_35ed13f7-5377-4795-9217-0a535ca85ed7" xlink:to="loc_us-gaap_ProceedsFromSaleOfOtherReceivables_86060f85-588f-40dd-8189-7d33c150c34a" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_AccountsReceivableFactored_b57cb462-634f-4c72-90cd-642fa897877d" xlink:href="ftre-20251231.xsd#ftre_AccountsReceivableFactored"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostLineItems_35ed13f7-5377-4795-9217-0a535ca85ed7" xlink:to="loc_ftre_AccountsReceivableFactored_b57cb462-634f-4c72-90cd-642fa897877d" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_ReceivableSecuritizationTerm_01b642ce-4e7d-4042-91fc-71950044f099" xlink:href="ftre-20251231.xsd#ftre_ReceivableSecuritizationTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostLineItems_35ed13f7-5377-4795-9217-0a535ca85ed7" xlink:to="loc_ftre_ReceivableSecuritizationTerm_01b642ce-4e7d-4042-91fc-71950044f099" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableFromSecuritization_7e315aab-442b-40ca-a426-e4afe9dea15e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccountsReceivableFromSecuritization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostLineItems_35ed13f7-5377-4795-9217-0a535ca85ed7" xlink:to="loc_us-gaap_AccountsReceivableFromSecuritization_7e315aab-442b-40ca-a426-e4afe9dea15e" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_AccountsReceivableFromSecuritizationSaleFees_18c8a250-ea43-46ec-992d-63ab0b8dd3d7" xlink:href="ftre-20251231.xsd#ftre_AccountsReceivableFromSecuritizationSaleFees"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostLineItems_35ed13f7-5377-4795-9217-0a535ca85ed7" xlink:to="loc_ftre_AccountsReceivableFromSecuritizationSaleFees_18c8a250-ea43-46ec-992d-63ab0b8dd3d7" xlink:type="arc" order="15"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fortrea.com/role/REVENUESNarrativeDetails_1" xlink:type="simple" xlink:href="ftre-20251231.xsd#REVENUESNarrativeDetails_1"/>
  <link:definitionLink xlink:role="http://www.fortrea.com/role/REVENUESNarrativeDetails_1" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostLineItems_35ed13f7-5377-4795-9217-0a535ca85ed7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CapitalizedContractCostLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostTable_8ba39edc-273f-4be8-88e3-6107bd27e38a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CapitalizedContractCostTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_CapitalizedContractCostLineItems_35ed13f7-5377-4795-9217-0a535ca85ed7" xlink:to="loc_us-gaap_CapitalizedContractCostTable_8ba39edc-273f-4be8-88e3-6107bd27e38a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostAxis_239a7c61-cbed-468a-8f6d-02fdec94535b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CapitalizedContractCostAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_CapitalizedContractCostTable_8ba39edc-273f-4be8-88e3-6107bd27e38a" xlink:to="loc_us-gaap_CapitalizedContractCostAxis_239a7c61-cbed-468a-8f6d-02fdec94535b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostDomain_239a7c61-cbed-468a-8f6d-02fdec94535b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CapitalizedContractCostDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CapitalizedContractCostAxis_239a7c61-cbed-468a-8f6d-02fdec94535b" xlink:to="loc_us-gaap_CapitalizedContractCostDomain_239a7c61-cbed-468a-8f6d-02fdec94535b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostDomain_9c200ef7-9d38-479e-b20f-3184c58d45c0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CapitalizedContractCostDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CapitalizedContractCostAxis_239a7c61-cbed-468a-8f6d-02fdec94535b" xlink:to="loc_us-gaap_CapitalizedContractCostDomain_9c200ef7-9d38-479e-b20f-3184c58d45c0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_SalesCommissionAssetsMember_6b693884-0015-405e-b806-30d164e4ca53" xlink:href="ftre-20251231.xsd#ftre_SalesCommissionAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostDomain_9c200ef7-9d38-479e-b20f-3184c58d45c0" xlink:to="loc_ftre_SalesCommissionAssetsMember_6b693884-0015-405e-b806-30d164e4ca53" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_DeferredContractCostsMember_1cef6842-ffcd-41ca-83f3-11da6e8c9417" xlink:href="ftre-20251231.xsd#ftre_DeferredContractCostsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostDomain_9c200ef7-9d38-479e-b20f-3184c58d45c0" xlink:to="loc_ftre_DeferredContractCostsMember_1cef6842-ffcd-41ca-83f3-11da6e8c9417" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_ba43c065-de2e-4fb1-a242-2de169a6b4ec" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_CapitalizedContractCostTable_8ba39edc-273f-4be8-88e3-6107bd27e38a" xlink:to="loc_srt_RangeAxis_ba43c065-de2e-4fb1-a242-2de169a6b4ec" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_ba43c065-de2e-4fb1-a242-2de169a6b4ec_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_ba43c065-de2e-4fb1-a242-2de169a6b4ec" xlink:to="loc_srt_RangeMember_ba43c065-de2e-4fb1-a242-2de169a6b4ec_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_c4df0200-f767-4709-adcf-fa60f5a906d4" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_ba43c065-de2e-4fb1-a242-2de169a6b4ec" xlink:to="loc_srt_RangeMember_c4df0200-f767-4709-adcf-fa60f5a906d4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_12f711c2-3f5f-445c-8612-15faba1a7983" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_c4df0200-f767-4709-adcf-fa60f5a906d4" xlink:to="loc_srt_MinimumMember_12f711c2-3f5f-445c-8612-15faba1a7983" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_fc6beb4c-39e6-4270-bf06-db671a371a6d" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_c4df0200-f767-4709-adcf-fa60f5a906d4" xlink:to="loc_srt_MaximumMember_fc6beb4c-39e6-4270-bf06-db671a371a6d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ChangeInAccountingEstimateByTypeAxis_c2977487-f7d0-4595-866c-b263ee5af2e7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ChangeInAccountingEstimateByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_CapitalizedContractCostTable_8ba39edc-273f-4be8-88e3-6107bd27e38a" xlink:to="loc_us-gaap_ChangeInAccountingEstimateByTypeAxis_c2977487-f7d0-4595-866c-b263ee5af2e7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ChangeInAccountingEstimateTypeDomain_c2977487-f7d0-4595-866c-b263ee5af2e7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ChangeInAccountingEstimateTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ChangeInAccountingEstimateByTypeAxis_c2977487-f7d0-4595-866c-b263ee5af2e7" xlink:to="loc_us-gaap_ChangeInAccountingEstimateTypeDomain_c2977487-f7d0-4595-866c-b263ee5af2e7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ChangeInAccountingEstimateTypeDomain_05bc745b-7e98-4b48-be32-1459a67b62b9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ChangeInAccountingEstimateTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ChangeInAccountingEstimateByTypeAxis_c2977487-f7d0-4595-866c-b263ee5af2e7" xlink:to="loc_us-gaap_ChangeInAccountingEstimateTypeDomain_05bc745b-7e98-4b48-be32-1459a67b62b9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_ChangeInScopeAndChangeInEstimatedEffortToCompleteContractMember_58944246-5c9f-4aac-9c6f-0acb5bba1892" xlink:href="ftre-20251231.xsd#ftre_ChangeInScopeAndChangeInEstimatedEffortToCompleteContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ChangeInAccountingEstimateTypeDomain_05bc745b-7e98-4b48-be32-1459a67b62b9" xlink:to="loc_ftre_ChangeInScopeAndChangeInEstimatedEffortToCompleteContractMember_58944246-5c9f-4aac-9c6f-0acb5bba1892" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostAmortization_6e6a4161-552a-492b-903d-2351ab6571a6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CapitalizedContractCostAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostLineItems_35ed13f7-5377-4795-9217-0a535ca85ed7" xlink:to="loc_us-gaap_CapitalizedContractCostAmortization_6e6a4161-552a-492b-903d-2351ab6571a6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_2f8d336b-26b3-4f92-a2f5-24a99f724478" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractWithCustomerLiabilityRevenueRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostLineItems_35ed13f7-5377-4795-9217-0a535ca85ed7" xlink:to="loc_us-gaap_ContractWithCustomerLiabilityRevenueRecognized_2f8d336b-26b3-4f92-a2f5-24a99f724478" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableSale_2d7b7ab3-2df8-48cc-9f49-a9547a6f664d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccountsReceivableSale"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostLineItems_35ed13f7-5377-4795-9217-0a535ca85ed7" xlink:to="loc_us-gaap_AccountsReceivableSale_2d7b7ab3-2df8-48cc-9f49-a9547a6f664d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligation_7b41647f-7c7d-40bd-a588-e83a9f5156bc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostLineItems_35ed13f7-5377-4795-9217-0a535ca85ed7" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligation_7b41647f-7c7d-40bd-a588-e83a9f5156bc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_c0e0e5cf-5d86-478e-a7fd-bea218458670" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostLineItems_35ed13f7-5377-4795-9217-0a535ca85ed7" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationPercentage_c0e0e5cf-5d86-478e-a7fd-bea218458670" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_f8d0b4f6-be29-4e27-9a25-9a0debb4964a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostLineItems_35ed13f7-5377-4795-9217-0a535ca85ed7" xlink:to="loc_us-gaap_RevenueRemainingPerformanceObligationExpectedTimingOfSatisfactionPeriod1_f8d0b4f6-be29-4e27-9a25-9a0debb4964a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerPerformanceObligationSatisfiedInPreviousPeriod_548f4ff4-09f9-4ea8-9c30-8801fa63c57c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractWithCustomerPerformanceObligationSatisfiedInPreviousPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostLineItems_35ed13f7-5377-4795-9217-0a535ca85ed7" xlink:to="loc_us-gaap_ContractWithCustomerPerformanceObligationSatisfiedInPreviousPeriod_548f4ff4-09f9-4ea8-9c30-8801fa63c57c" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_d8215e29-1eb3-4a16-a3ee-144eee6624cf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostLineItems_35ed13f7-5377-4795-9217-0a535ca85ed7" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_d8215e29-1eb3-4a16-a3ee-144eee6624cf" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_a65653ed-d41a-46ae-875a-2f45d2117190" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostLineItems_35ed13f7-5377-4795-9217-0a535ca85ed7" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_a65653ed-d41a-46ae-875a-2f45d2117190" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasic_3e9a5f0c-de57-42b5-b41e-e20e84809ea2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EarningsPerShareBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostLineItems_35ed13f7-5377-4795-9217-0a535ca85ed7" xlink:to="loc_us-gaap_EarningsPerShareBasic_3e9a5f0c-de57-42b5-b41e-e20e84809ea2" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_AccountsReceivablePurchaseProgramMaximumFacilityAmount_2f40f0d0-52e0-403b-8070-e3f2077b4114" xlink:href="ftre-20251231.xsd#ftre_AccountsReceivablePurchaseProgramMaximumFacilityAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostLineItems_35ed13f7-5377-4795-9217-0a535ca85ed7" xlink:to="loc_ftre_AccountsReceivablePurchaseProgramMaximumFacilityAmount_2f40f0d0-52e0-403b-8070-e3f2077b4114" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromSaleOfOtherReceivables_86060f85-588f-40dd-8189-7d33c150c34a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProceedsFromSaleOfOtherReceivables"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostLineItems_35ed13f7-5377-4795-9217-0a535ca85ed7" xlink:to="loc_us-gaap_ProceedsFromSaleOfOtherReceivables_86060f85-588f-40dd-8189-7d33c150c34a" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_AccountsReceivableFactored_b57cb462-634f-4c72-90cd-642fa897877d" xlink:href="ftre-20251231.xsd#ftre_AccountsReceivableFactored"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostLineItems_35ed13f7-5377-4795-9217-0a535ca85ed7" xlink:to="loc_ftre_AccountsReceivableFactored_b57cb462-634f-4c72-90cd-642fa897877d" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_ReceivableSecuritizationTerm_01b642ce-4e7d-4042-91fc-71950044f099" xlink:href="ftre-20251231.xsd#ftre_ReceivableSecuritizationTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostLineItems_35ed13f7-5377-4795-9217-0a535ca85ed7" xlink:to="loc_ftre_ReceivableSecuritizationTerm_01b642ce-4e7d-4042-91fc-71950044f099" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableFromSecuritization_7e315aab-442b-40ca-a426-e4afe9dea15e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccountsReceivableFromSecuritization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostLineItems_35ed13f7-5377-4795-9217-0a535ca85ed7" xlink:to="loc_us-gaap_AccountsReceivableFromSecuritization_7e315aab-442b-40ca-a426-e4afe9dea15e" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_AccountsReceivableFromSecuritizationSaleFees_18c8a250-ea43-46ec-992d-63ab0b8dd3d7" xlink:href="ftre-20251231.xsd#ftre_AccountsReceivableFromSecuritizationSaleFees"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostLineItems_35ed13f7-5377-4795-9217-0a535ca85ed7" xlink:to="loc_ftre_AccountsReceivableFromSecuritizationSaleFees_18c8a250-ea43-46ec-992d-63ab0b8dd3d7" xlink:type="arc" order="15"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fortrea.com/role/RESTRUCTURINGANDOTHERCHARGESNarrativeDetails" xlink:type="simple" xlink:href="ftre-20251231.xsd#RESTRUCTURINGANDOTHERCHARGESNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.fortrea.com/role/RESTRUCTURINGANDOTHERCHARGESNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveLineItems_150e51f7-fcac-48c3-b48f-3dcc8f949b63" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringCostAndReserveLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_06c556c1-2b97-4b6b-8266-1808012f2aa6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfRestructuringAndRelatedCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_150e51f7-fcac-48c3-b48f-3dcc8f949b63" xlink:to="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_06c556c1-2b97-4b6b-8266-1808012f2aa6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveAxis_b880d75c-1cce-4ad5-8098-f50926ac6198" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringCostAndReserveAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_06c556c1-2b97-4b6b-8266-1808012f2aa6" xlink:to="loc_us-gaap_RestructuringCostAndReserveAxis_b880d75c-1cce-4ad5-8098-f50926ac6198" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_b880d75c-1cce-4ad5-8098-f50926ac6198_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_b880d75c-1cce-4ad5-8098-f50926ac6198" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_b880d75c-1cce-4ad5-8098-f50926ac6198_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_fe3030ab-b4da-4242-8a6c-8da9d7ce96a1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_b880d75c-1cce-4ad5-8098-f50926ac6198" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_fe3030ab-b4da-4242-8a6c-8da9d7ce96a1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeSeveranceMember_c0e5db6d-7616-45b6-b1e3-dca7d14c57c0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeSeveranceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_fe3030ab-b4da-4242-8a6c-8da9d7ce96a1" xlink:to="loc_us-gaap_EmployeeSeveranceMember_c0e5db6d-7616-45b6-b1e3-dca7d14c57c0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_FacilityAndOtherCostMember_019c1be8-e170-7f04-98a2-be5019c1416d" xlink:href="ftre-20251231.xsd#ftre_FacilityAndOtherCostMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_fe3030ab-b4da-4242-8a6c-8da9d7ce96a1" xlink:to="loc_ftre_FacilityAndOtherCostMember_019c1be8-e170-7f04-98a2-be5019c1416d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_FacilityCostMember_8d6bb880-7041-4161-af06-17cd50ec4206" xlink:href="ftre-20251231.xsd#ftre_FacilityCostMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_fe3030ab-b4da-4242-8a6c-8da9d7ce96a1" xlink:to="loc_ftre_FacilityCostMember_8d6bb880-7041-4161-af06-17cd50ec4206" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanAxis_f3f8382c-c616-4a72-b1fc-1c2a4f2a93a5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringPlanAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_06c556c1-2b97-4b6b-8266-1808012f2aa6" xlink:to="loc_us-gaap_RestructuringPlanAxis_f3f8382c-c616-4a72-b1fc-1c2a4f2a93a5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanDomain_f3f8382c-c616-4a72-b1fc-1c2a4f2a93a5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringPlanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringPlanAxis_f3f8382c-c616-4a72-b1fc-1c2a4f2a93a5" xlink:to="loc_us-gaap_RestructuringPlanDomain_f3f8382c-c616-4a72-b1fc-1c2a4f2a93a5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringPlanDomain_81f6f218-9517-4606-b755-db514df6c7b1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringPlanDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringPlanAxis_f3f8382c-c616-4a72-b1fc-1c2a4f2a93a5" xlink:to="loc_us-gaap_RestructuringPlanDomain_81f6f218-9517-4606-b755-db514df6c7b1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_A2025RestructuringPlanMember_a732b083-3425-4bcb-9738-d2ddeb7dea27" xlink:href="ftre-20251231.xsd#ftre_A2025RestructuringPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringPlanDomain_81f6f218-9517-4606-b755-db514df6c7b1" xlink:to="loc_ftre_A2025RestructuringPlanMember_a732b083-3425-4bcb-9738-d2ddeb7dea27" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_A2024RestructuringPlanMember_8b70393b-3094-429d-b0b9-929efec81263" xlink:href="ftre-20251231.xsd#ftre_A2024RestructuringPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringPlanDomain_81f6f218-9517-4606-b755-db514df6c7b1" xlink:to="loc_ftre_A2024RestructuringPlanMember_8b70393b-3094-429d-b0b9-929efec81263" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_A2023RestructuringPlanMember_4621cce0-5d06-41b8-a881-22c1a027d32c" xlink:href="ftre-20251231.xsd#ftre_A2023RestructuringPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringPlanDomain_81f6f218-9517-4606-b755-db514df6c7b1" xlink:to="loc_ftre_A2023RestructuringPlanMember_4621cce0-5d06-41b8-a881-22c1a027d32c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeveranceCosts1_093c486f-b9b1-4c9e-b10a-ecd969e56ca0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SeveranceCosts1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_150e51f7-fcac-48c3-b48f-3dcc8f949b63" xlink:to="loc_us-gaap_SeveranceCosts1_093c486f-b9b1-4c9e-b10a-ecd969e56ca0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringAndRelatedCostIncurredCost_ae7db0b8-5639-405f-ae3b-10ae253a330d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringAndRelatedCostIncurredCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_150e51f7-fcac-48c3-b48f-3dcc8f949b63" xlink:to="loc_us-gaap_RestructuringAndRelatedCostIncurredCost_ae7db0b8-5639-405f-ae3b-10ae253a330d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostsAndAssetImpairmentCharges_019be5ef-4048-7392-a428-6e3af84ed57b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringCostsAndAssetImpairmentCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_150e51f7-fcac-48c3-b48f-3dcc8f949b63" xlink:to="loc_us-gaap_RestructuringCostsAndAssetImpairmentCharges_019be5ef-4048-7392-a428-6e3af84ed57b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherRestructuringCosts_1d3c695e-6f03-4577-ad55-1034c434bcd5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherRestructuringCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_150e51f7-fcac-48c3-b48f-3dcc8f949b63" xlink:to="loc_us-gaap_OtherRestructuringCosts_1d3c695e-6f03-4577-ad55-1034c434bcd5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserveAccrualAdjustment1_ea2c1cf7-c0f4-43f9-8873-2c35f1f5bc22" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringReserveAccrualAdjustment1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_150e51f7-fcac-48c3-b48f-3dcc8f949b63" xlink:to="loc_us-gaap_RestructuringReserveAccrualAdjustment1_ea2c1cf7-c0f4-43f9-8873-2c35f1f5bc22" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fortrea.com/role/RESTRUCTURINGANDOTHERCHARGESScheduleofRestructuringAccrualActivitiesDetails" xlink:type="simple" xlink:href="ftre-20251231.xsd#RESTRUCTURINGANDOTHERCHARGESScheduleofRestructuringAccrualActivitiesDetails"/>
  <link:definitionLink xlink:role="http://www.fortrea.com/role/RESTRUCTURINGANDOTHERCHARGESScheduleofRestructuringAccrualActivitiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveLineItems_786811cc-1828-4528-abd0-ed47e3c7ab1a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringCostAndReserveLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_d8f5dfd7-98b2-486e-972c-2080db60d3c5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfRestructuringAndRelatedCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_786811cc-1828-4528-abd0-ed47e3c7ab1a" xlink:to="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_d8f5dfd7-98b2-486e-972c-2080db60d3c5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCostAndReserveAxis_f12e8e79-3fd8-4639-9e36-2807519dd426" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringCostAndReserveAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRestructuringAndRelatedCostsTable_d8f5dfd7-98b2-486e-972c-2080db60d3c5" xlink:to="loc_us-gaap_RestructuringCostAndReserveAxis_f12e8e79-3fd8-4639-9e36-2807519dd426" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_f12e8e79-3fd8-4639-9e36-2807519dd426_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_f12e8e79-3fd8-4639-9e36-2807519dd426" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_f12e8e79-3fd8-4639-9e36-2807519dd426_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfRestructuringDomain_1af4245e-1ec2-4cee-8855-050e68888530" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TypeOfRestructuringDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RestructuringCostAndReserveAxis_f12e8e79-3fd8-4639-9e36-2807519dd426" xlink:to="loc_us-gaap_TypeOfRestructuringDomain_1af4245e-1ec2-4cee-8855-050e68888530" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeSeveranceMember_b8685704-8226-4399-9d46-f159efb706a1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeSeveranceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_1af4245e-1ec2-4cee-8855-050e68888530" xlink:to="loc_us-gaap_EmployeeSeveranceMember_b8685704-8226-4399-9d46-f159efb706a1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_FacilityCostMember_9150aff2-6c0d-43b2-9119-7739b376c4ad" xlink:href="ftre-20251231.xsd#ftre_FacilityCostMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TypeOfRestructuringDomain_1af4245e-1ec2-4cee-8855-050e68888530" xlink:to="loc_ftre_FacilityCostMember_9150aff2-6c0d-43b2-9119-7739b376c4ad" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserveRollForward_6b227b60-4367-4492-99eb-20942e4da49b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringReserveRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringCostAndReserveLineItems_786811cc-1828-4528-abd0-ed47e3c7ab1a" xlink:to="loc_us-gaap_RestructuringReserveRollForward_6b227b60-4367-4492-99eb-20942e4da49b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserve_965c47ba-7139-4928-bb3c-cbb8eb2aa2fa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringReserve"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringReserveRollForward_6b227b60-4367-4492-99eb-20942e4da49b" xlink:to="loc_us-gaap_RestructuringReserve_965c47ba-7139-4928-bb3c-cbb8eb2aa2fa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringCharges_e70704c2-1b9b-4f10-b8c3-4c8828eccad2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringReserveRollForward_6b227b60-4367-4492-99eb-20942e4da49b" xlink:to="loc_us-gaap_RestructuringCharges_e70704c2-1b9b-4f10-b8c3-4c8828eccad2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserveAccrualAdjustment1_4fe165d3-646d-4622-9b1f-c94b57c1df92" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringReserveAccrualAdjustment1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringReserveRollForward_6b227b60-4367-4492-99eb-20942e4da49b" xlink:to="loc_us-gaap_RestructuringReserveAccrualAdjustment1_4fe165d3-646d-4622-9b1f-c94b57c1df92" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_RestructuringReservePaymentAndOtherAdjustments_c080b81b-b754-4bd6-803a-0f44712a3a4b" xlink:href="ftre-20251231.xsd#ftre_RestructuringReservePaymentAndOtherAdjustments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringReserveRollForward_6b227b60-4367-4492-99eb-20942e4da49b" xlink:to="loc_ftre_RestructuringReservePaymentAndOtherAdjustments_c080b81b-b754-4bd6-803a-0f44712a3a4b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringReserve_d24ce4c8-dbf6-45e5-9836-6c63e7bf9bfd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringReserve"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringIncurredCostStatementOfIncomeOrComprehensiveIncomeExtensibleEnumeration_84be6fe3-7249-40b9-aa1d-c0ace38f1926" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringIncurredCostStatementOfIncomeOrComprehensiveIncomeExtensibleEnumeration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestructuringReserveRollForward_6b227b60-4367-4492-99eb-20942e4da49b" xlink:to="loc_us-gaap_RestructuringIncurredCostStatementOfIncomeOrComprehensiveIncomeExtensibleEnumeration_84be6fe3-7249-40b9-aa1d-c0ace38f1926" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fortrea.com/role/EARNINGSLOSSPERSHAREReconciliationofBasicEarningsperSharetoDilutedEarningsperShareDetails" xlink:type="simple" xlink:href="ftre-20251231.xsd#EARNINGSLOSSPERSHAREReconciliationofBasicEarningsperSharetoDilutedEarningsperShareDetails"/>
  <link:definitionLink xlink:role="http://www.fortrea.com/role/EARNINGSLOSSPERSHAREReconciliationofBasicEarningsperSharetoDilutedEarningsperShareDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasicLineItems_68ec7676-2333-4916-84a4-2727abf883f3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EarningsPerShareBasicLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEarningsPerShareBasicByCommonClassTable_458c343f-2c32-4720-b54c-fe84dab1f576" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfEarningsPerShareBasicByCommonClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EarningsPerShareBasicLineItems_68ec7676-2333-4916-84a4-2727abf883f3" xlink:to="loc_us-gaap_ScheduleOfEarningsPerShareBasicByCommonClassTable_458c343f-2c32-4720-b54c-fe84dab1f576" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementOperatingActivitiesSegmentAxis_cffab910-b48a-425d-993c-6370ff071b73" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementOperatingActivitiesSegmentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEarningsPerShareBasicByCommonClassTable_458c343f-2c32-4720-b54c-fe84dab1f576" xlink:to="loc_us-gaap_StatementOperatingActivitiesSegmentAxis_cffab910-b48a-425d-993c-6370ff071b73" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentOperatingActivitiesDomain_cffab910-b48a-425d-993c-6370ff071b73_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentOperatingActivitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementOperatingActivitiesSegmentAxis_cffab910-b48a-425d-993c-6370ff071b73" xlink:to="loc_us-gaap_SegmentOperatingActivitiesDomain_cffab910-b48a-425d-993c-6370ff071b73_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentOperatingActivitiesDomain_a552ef42-6e05-46c6-bbdf-c08fd863f2d6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentOperatingActivitiesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementOperatingActivitiesSegmentAxis_cffab910-b48a-425d-993c-6370ff071b73" xlink:to="loc_us-gaap_SegmentOperatingActivitiesDomain_a552ef42-6e05-46c6-bbdf-c08fd863f2d6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentContinuingOperationsMember_d483bd1c-ab14-4e51-80c3-4b0cd9b4c847" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentContinuingOperationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentOperatingActivitiesDomain_a552ef42-6e05-46c6-bbdf-c08fd863f2d6" xlink:to="loc_us-gaap_SegmentContinuingOperationsMember_d483bd1c-ab14-4e51-80c3-4b0cd9b4c847" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDiscontinuedOperationsMember_e70b4b65-310c-47f6-b248-3b9c16059043" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDiscontinuedOperationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentOperatingActivitiesDomain_a552ef42-6e05-46c6-bbdf-c08fd863f2d6" xlink:to="loc_us-gaap_SegmentDiscontinuedOperationsMember_e70b4b65-310c-47f6-b248-3b9c16059043" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsAttributableToParentAbstract_e9ce9d22-1edb-4c23-bb1c-e013e2a6b33e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeLossFromContinuingOperationsAttributableToParentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicLineItems_68ec7676-2333-4916-84a4-2727abf883f3" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsAttributableToParentAbstract_e9ce9d22-1edb-4c23-bb1c-e013e2a6b33e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperations_c66d368e-488a-48c9-b12a-0fc61f4a0864" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeLossFromContinuingOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeLossFromContinuingOperationsAttributableToParentAbstract_e9ce9d22-1edb-4c23-bb1c-e013e2a6b33e" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperations_c66d368e-488a-48c9-b12a-0fc61f4a0864" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossFromContinuingOperationsAvailableToCommonShareholdersDiluted_4a5a7e31-a370-4725-9b66-1fe89d0103c3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetIncomeLossFromContinuingOperationsAvailableToCommonShareholdersDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeLossFromContinuingOperationsAttributableToParentAbstract_e9ce9d22-1edb-4c23-bb1c-e013e2a6b33e" xlink:to="loc_us-gaap_NetIncomeLossFromContinuingOperationsAvailableToCommonShareholdersDiluted_4a5a7e31-a370-4725-9b66-1fe89d0103c3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_c05ab3ee-5424-4376-936b-fd3b7afec54e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeLossFromContinuingOperationsAttributableToParentAbstract_e9ce9d22-1edb-4c23-bb1c-e013e2a6b33e" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_c05ab3ee-5424-4376-936b-fd3b7afec54e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_62164b3f-d777-4f63-9d17-a9c625f85fb3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeLossFromContinuingOperationsAttributableToParentAbstract_e9ce9d22-1edb-4c23-bb1c-e013e2a6b33e" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_62164b3f-d777-4f63-9d17-a9c625f85fb3" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsPerBasicShare_6d6ce297-f150-4501-822d-20d1129d73ec" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeLossFromContinuingOperationsPerBasicShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeLossFromContinuingOperationsAttributableToParentAbstract_e9ce9d22-1edb-4c23-bb1c-e013e2a6b33e" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsPerBasicShare_6d6ce297-f150-4501-822d-20d1129d73ec" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsPerDilutedShare_c19d4271-b6ff-4d02-b9cb-bafefc0395df" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeLossFromContinuingOperationsPerDilutedShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeLossFromContinuingOperationsAttributableToParentAbstract_e9ce9d22-1edb-4c23-bb1c-e013e2a6b33e" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsPerDilutedShare_c19d4271-b6ff-4d02-b9cb-bafefc0395df" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntityAbstract_70fb03ff-8bce-44c1-aef3-006c86ef750a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicLineItems_68ec7676-2333-4916-84a4-2727abf883f3" xlink:to="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntityAbstract_70fb03ff-8bce-44c1-aef3-006c86ef750a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity_2c82763e-55ee-4116-9b8f-e49a81561bd8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntityAbstract_70fb03ff-8bce-44c1-aef3-006c86ef750a" xlink:to="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity_2c82763e-55ee-4116-9b8f-e49a81561bd8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossFromDiscontinuedOperationsAvailableToCommonShareholdersDiluted_8d0d7d8d-40c3-49ff-a7d7-2ce9c9c8aad6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetIncomeLossFromDiscontinuedOperationsAvailableToCommonShareholdersDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntityAbstract_70fb03ff-8bce-44c1-aef3-006c86ef750a" xlink:to="loc_us-gaap_NetIncomeLossFromDiscontinuedOperationsAvailableToCommonShareholdersDiluted_8d0d7d8d-40c3-49ff-a7d7-2ce9c9c8aad6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_34bbf71a-a8ef-49e9-8666-02ff1ab7a28e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_686e4bd1-fa84-4e9f-90f0-bb0128cca06c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxPerBasicShare_f5c76c6a-322a-4d77-88db-78a759ff1a1b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxPerBasicShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntityAbstract_70fb03ff-8bce-44c1-aef3-006c86ef750a" xlink:to="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxPerBasicShare_f5c76c6a-322a-4d77-88db-78a759ff1a1b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxPerDilutedShare_b00c8010-9684-45e9-929a-0e3586583a22" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxPerDilutedShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntityAbstract_70fb03ff-8bce-44c1-aef3-006c86ef750a" xlink:to="loc_us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxPerDilutedShare_b00c8010-9684-45e9-929a-0e3586583a22" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fortrea.com/role/EARNINGSLOSSPERSHAREAntidilutiveSecuritiesExcludedfromComputationDetails" xlink:type="simple" xlink:href="ftre-20251231.xsd#EARNINGSLOSSPERSHAREAntidilutiveSecuritiesExcludedfromComputationDetails"/>
  <link:definitionLink xlink:role="http://www.fortrea.com/role/EARNINGSLOSSPERSHAREAntidilutiveSecuritiesExcludedfromComputationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_b491f2fa-6a61-412a-94da-e9a7aea420ae" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_265908e6-dab2-4545-8e17-1103ea0574c5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_b491f2fa-6a61-412a-94da-e9a7aea420ae" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_265908e6-dab2-4545-8e17-1103ea0574c5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_37ae6280-246c-4a9d-b2f6-b996905d680f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_265908e6-dab2-4545-8e17-1103ea0574c5" xlink:to="loc_us-gaap_AwardTypeAxis_37ae6280-246c-4a9d-b2f6-b996905d680f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_37ae6280-246c-4a9d-b2f6-b996905d680f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_37ae6280-246c-4a9d-b2f6-b996905d680f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_37ae6280-246c-4a9d-b2f6-b996905d680f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_3df13723-9ca6-4d65-a395-87493aa1b2ba" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_37ae6280-246c-4a9d-b2f6-b996905d680f" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_3df13723-9ca6-4d65-a395-87493aa1b2ba" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_720c0cb0-9e64-45d0-ba37-8bcb16737d61" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_3df13723-9ca6-4d65-a395-87493aa1b2ba" xlink:to="loc_us-gaap_EmployeeStockOptionMember_720c0cb0-9e64-45d0-ba37-8bcb16737d61" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_d585e91b-23b3-4ddb-a1e2-50d2481a1889" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_265908e6-dab2-4545-8e17-1103ea0574c5" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_d585e91b-23b3-4ddb-a1e2-50d2481a1889" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_d585e91b-23b3-4ddb-a1e2-50d2481a1889_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_d585e91b-23b3-4ddb-a1e2-50d2481a1889" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_d585e91b-23b3-4ddb-a1e2-50d2481a1889_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_e645104a-425a-4f53-a781-4df746e5d5da" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_d585e91b-23b3-4ddb-a1e2-50d2481a1889" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_e645104a-425a-4f53-a781-4df746e5d5da" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_8efbbd59-d4f6-42ae-81e5-365b58059a35" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_e645104a-425a-4f53-a781-4df746e5d5da" xlink:to="loc_us-gaap_EmployeeStockOptionMember_8efbbd59-d4f6-42ae-81e5-365b58059a35" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_cf8ceab0-e398-4854-92b9-70a3a768a131" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_b491f2fa-6a61-412a-94da-e9a7aea420ae" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_cf8ceab0-e398-4854-92b9-70a3a768a131" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_1386d5f4-6b55-486c-94e5-f9a42e7b17b6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_b491f2fa-6a61-412a-94da-e9a7aea420ae" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_1386d5f4-6b55-486c-94e5-f9a42e7b17b6" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fortrea.com/role/LEASESNarrativeDetails" xlink:type="simple" xlink:href="ftre-20251231.xsd#LEASESNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.fortrea.com/role/LEASESNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionLineItems_614ba0f1-4b6e-46f9-b645-173a4cc2af1d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LesseeLeaseDescriptionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeLeaseDescriptionTable_0f4aefac-a09d-4d7c-84ec-d889c713a721" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LesseeLeaseDescriptionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_614ba0f1-4b6e-46f9-b645-173a4cc2af1d" xlink:to="loc_us-gaap_LesseeLeaseDescriptionTable_0f4aefac-a09d-4d7c-84ec-d889c713a721" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_bcee79fe-87d7-4724-ae79-3b09071066cd" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LesseeLeaseDescriptionTable_0f4aefac-a09d-4d7c-84ec-d889c713a721" xlink:to="loc_srt_RangeAxis_bcee79fe-87d7-4724-ae79-3b09071066cd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_bcee79fe-87d7-4724-ae79-3b09071066cd_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_bcee79fe-87d7-4724-ae79-3b09071066cd" xlink:to="loc_srt_RangeMember_bcee79fe-87d7-4724-ae79-3b09071066cd_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_82bc94fc-c07b-4c29-9456-59ae7f081e81" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_bcee79fe-87d7-4724-ae79-3b09071066cd" xlink:to="loc_srt_RangeMember_82bc94fc-c07b-4c29-9456-59ae7f081e81" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_9f202196-db95-4ce7-91b5-2777e7797b93" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_82bc94fc-c07b-4c29-9456-59ae7f081e81" xlink:to="loc_srt_MinimumMember_9f202196-db95-4ce7-91b5-2777e7797b93" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_44625cd0-ad63-4809-a91f-6fbcdf187c05" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_82bc94fc-c07b-4c29-9456-59ae7f081e81" xlink:to="loc_srt_MaximumMember_44625cd0-ad63-4809-a91f-6fbcdf187c05" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseRemainingLeaseTerm_4732a026-3816-400a-b08b-89e4a2437286" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LesseeOperatingLeaseRemainingLeaseTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_614ba0f1-4b6e-46f9-b645-173a4cc2af1d" xlink:to="loc_us-gaap_LesseeOperatingLeaseRemainingLeaseTerm_4732a026-3816-400a-b08b-89e4a2437286" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LesseeOperatingLeaseRenewalTerm_b95d182d-a222-4f71-82c1-969da6abfcd1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LesseeOperatingLeaseRenewalTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_614ba0f1-4b6e-46f9-b645-173a4cc2af1d" xlink:to="loc_us-gaap_LesseeOperatingLeaseRenewalTerm_b95d182d-a222-4f71-82c1-969da6abfcd1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermLeaseCost_cb313454-bb99-42dd-a951-dbe4a1d6a1e7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShortTermLeaseCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_614ba0f1-4b6e-46f9-b645-173a4cc2af1d" xlink:to="loc_us-gaap_ShortTermLeaseCost_cb313454-bb99-42dd-a951-dbe4a1d6a1e7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubleaseIncome_fc727e91-5d77-4959-828a-79fedb7eef9c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SubleaseIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_614ba0f1-4b6e-46f9-b645-173a4cc2af1d" xlink:to="loc_us-gaap_SubleaseIncome_fc727e91-5d77-4959-828a-79fedb7eef9c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableLeasePayment_4896d1d3-df2c-42b5-81e4-48d57cb17dcf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VariableLeasePayment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LesseeLeaseDescriptionLineItems_614ba0f1-4b6e-46f9-b645-173a4cc2af1d" xlink:to="loc_us-gaap_VariableLeasePayment_4896d1d3-df2c-42b5-81e4-48d57cb17dcf" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fortrea.com/role/PROPERTYPLANTANDEQUIPMENTNETScheduleofPropertyPlantandEquipmentDetails" xlink:type="simple" xlink:href="ftre-20251231.xsd#PROPERTYPLANTANDEQUIPMENTNETScheduleofPropertyPlantandEquipmentDetails"/>
  <link:definitionLink xlink:role="http://www.fortrea.com/role/PROPERTYPLANTANDEQUIPMENTNETScheduleofPropertyPlantandEquipmentDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_281d23b3-6c95-4399-bfa3-4c4b38e96467" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_0fc5991f-71b0-4f55-b092-063e8b8d5a4e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_281d23b3-6c95-4399-bfa3-4c4b38e96467" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_0fc5991f-71b0-4f55-b092-063e8b8d5a4e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_7e2e38eb-001d-45ab-b542-dab909da5aa8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_0fc5991f-71b0-4f55-b092-063e8b8d5a4e" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_7e2e38eb-001d-45ab-b542-dab909da5aa8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_7e2e38eb-001d-45ab-b542-dab909da5aa8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_7e2e38eb-001d-45ab-b542-dab909da5aa8" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_7e2e38eb-001d-45ab-b542-dab909da5aa8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_e1eb582c-645b-4d00-927a-91abe8e3a988" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_7e2e38eb-001d-45ab-b542-dab909da5aa8" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_e1eb582c-645b-4d00-927a-91abe8e3a988" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_BuildingsAndLeaseholdImprovementsMember_2ca93355-57c7-43db-ad3b-d89fadec9f57" xlink:href="ftre-20251231.xsd#ftre_BuildingsAndLeaseholdImprovementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_e1eb582c-645b-4d00-927a-91abe8e3a988" xlink:to="loc_ftre_BuildingsAndLeaseholdImprovementsMember_2ca93355-57c7-43db-ad3b-d89fadec9f57" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SoftwareAndSoftwareDevelopmentCostsMember_514fba4e-454c-4b34-b6d0-07c0832e3bbe" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SoftwareAndSoftwareDevelopmentCostsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_e1eb582c-645b-4d00-927a-91abe8e3a988" xlink:to="loc_us-gaap_SoftwareAndSoftwareDevelopmentCostsMember_514fba4e-454c-4b34-b6d0-07c0832e3bbe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MachineryAndEquipmentMember_53df0301-713a-45e3-bce2-7c78b1ed9c45" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MachineryAndEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_e1eb582c-645b-4d00-927a-91abe8e3a988" xlink:to="loc_us-gaap_MachineryAndEquipmentMember_53df0301-713a-45e3-bce2-7c78b1ed9c45" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FurnitureAndFixturesMember_142794c3-8ef2-4b4c-984c-596d09c195ee" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FurnitureAndFixturesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_e1eb582c-645b-4d00-927a-91abe8e3a988" xlink:to="loc_us-gaap_FurnitureAndFixturesMember_142794c3-8ef2-4b4c-984c-596d09c195ee" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConstructionInProgressMember_2a59b694-5b39-4a07-afeb-916ef6b47414" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConstructionInProgressMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_e1eb582c-645b-4d00-927a-91abe8e3a988" xlink:to="loc_us-gaap_ConstructionInProgressMember_2a59b694-5b39-4a07-afeb-916ef6b47414" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_a7d6670b-0267-483c-9dd7-f1c2770158c2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_281d23b3-6c95-4399-bfa3-4c4b38e96467" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_a7d6670b-0267-483c-9dd7-f1c2770158c2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseRightOfUseAsset_42927c33-2bbb-475c-a647-893e89ca8ce2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingLeaseRightOfUseAsset"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_281d23b3-6c95-4399-bfa3-4c4b38e96467" xlink:to="loc_us-gaap_OperatingLeaseRightOfUseAsset_42927c33-2bbb-475c-a647-893e89ca8ce2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_PropertyPlantAndEquipmentAndOperatingLeaseRightOfUseAssetBeforeAccumulatedDepreciationAndAmortization_61e4cde2-5761-4e03-93b2-ac3dc3e7c50d" xlink:href="ftre-20251231.xsd#ftre_PropertyPlantAndEquipmentAndOperatingLeaseRightOfUseAssetBeforeAccumulatedDepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_281d23b3-6c95-4399-bfa3-4c4b38e96467" xlink:to="loc_ftre_PropertyPlantAndEquipmentAndOperatingLeaseRightOfUseAssetBeforeAccumulatedDepreciationAndAmortization_61e4cde2-5761-4e03-93b2-ac3dc3e7c50d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_PropertyPlantAndEquipmentAndOperatingLeaseRightOfUseAssetAccumulatedDepreciationAndAmortization_fe88aa52-2aa3-48a0-a5d1-71b154c959b9" xlink:href="ftre-20251231.xsd#ftre_PropertyPlantAndEquipmentAndOperatingLeaseRightOfUseAssetAccumulatedDepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_281d23b3-6c95-4399-bfa3-4c4b38e96467" xlink:to="loc_ftre_PropertyPlantAndEquipmentAndOperatingLeaseRightOfUseAssetAccumulatedDepreciationAndAmortization_fe88aa52-2aa3-48a0-a5d1-71b154c959b9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_PropertyPlantAndEquipmentAndOperatingLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization_59f8b5ff-36a0-4723-9c41-4ff7bf984c83" xlink:href="ftre-20251231.xsd#ftre_PropertyPlantAndEquipmentAndOperatingLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_281d23b3-6c95-4399-bfa3-4c4b38e96467" xlink:to="loc_ftre_PropertyPlantAndEquipmentAndOperatingLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization_59f8b5ff-36a0-4723-9c41-4ff7bf984c83" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fortrea.com/role/PROPERTYPLANTANDEQUIPMENTNETNarrativeDetails" xlink:type="simple" xlink:href="ftre-20251231.xsd#PROPERTYPLANTANDEQUIPMENTNETNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.fortrea.com/role/PROPERTYPLANTANDEQUIPMENTNETNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_c79bf018-7502-4787-8a74-7d5ba2eaf1fa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_fe8797d2-9dd9-4792-bfd7-5507edb1ad23" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_c79bf018-7502-4787-8a74-7d5ba2eaf1fa" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_fe8797d2-9dd9-4792-bfd7-5507edb1ad23" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_24c51b67-a5e9-49f1-9d4b-aabc0c6ffb1e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_fe8797d2-9dd9-4792-bfd7-5507edb1ad23" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_24c51b67-a5e9-49f1-9d4b-aabc0c6ffb1e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_24c51b67-a5e9-49f1-9d4b-aabc0c6ffb1e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_24c51b67-a5e9-49f1-9d4b-aabc0c6ffb1e" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_24c51b67-a5e9-49f1-9d4b-aabc0c6ffb1e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_bb19630c-5957-4653-a910-58bb3a648f73" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_24c51b67-a5e9-49f1-9d4b-aabc0c6ffb1e" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_bb19630c-5957-4653-a910-58bb3a648f73" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SoftwareAndSoftwareDevelopmentCostsMember_7ddf0989-5bfc-4374-83aa-a88b09f80b0b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SoftwareAndSoftwareDevelopmentCostsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_bb19630c-5957-4653-a910-58bb3a648f73" xlink:to="loc_us-gaap_SoftwareAndSoftwareDevelopmentCostsMember_7ddf0989-5bfc-4374-83aa-a88b09f80b0b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Depreciation_3dd75ba8-666c-4c6c-ad5f-4d0013a7aa86" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Depreciation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_c79bf018-7502-4787-8a74-7d5ba2eaf1fa" xlink:to="loc_us-gaap_Depreciation_3dd75ba8-666c-4c6c-ad5f-4d0013a7aa86" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fortrea.com/role/PROPERTYPLANTANDEQUIPMENTNETScheduleofPropertyPlantandEquipmentbyGeographicAreasDetails" xlink:type="simple" xlink:href="ftre-20251231.xsd#PROPERTYPLANTANDEQUIPMENTNETScheduleofPropertyPlantandEquipmentbyGeographicAreasDetails"/>
  <link:definitionLink xlink:role="http://www.fortrea.com/role/PROPERTYPLANTANDEQUIPMENTNETScheduleofPropertyPlantandEquipmentbyGeographicAreasDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_5fbf1e44-6aa5-4ca5-b999-49ac83c5211f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_fd1b55b4-8720-4dbe-b328-f6cfb1c60f6d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_5fbf1e44-6aa5-4ca5-b999-49ac83c5211f" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_fd1b55b4-8720-4dbe-b328-f6cfb1c60f6d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_0867708f-90ba-4bcf-a516-3da7311788f8" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_fd1b55b4-8720-4dbe-b328-f6cfb1c60f6d" xlink:to="loc_srt_StatementGeographicalAxis_0867708f-90ba-4bcf-a516-3da7311788f8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_0867708f-90ba-4bcf-a516-3da7311788f8_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_0867708f-90ba-4bcf-a516-3da7311788f8" xlink:to="loc_srt_SegmentGeographicalDomain_0867708f-90ba-4bcf-a516-3da7311788f8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_fd0ce648-4e1c-4fb8-8d68-7030d7b8919a" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_0867708f-90ba-4bcf-a516-3da7311788f8" xlink:to="loc_srt_SegmentGeographicalDomain_fd0ce648-4e1c-4fb8-8d68-7030d7b8919a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NorthAmericaMember_f5fcbc7a-fd3b-4e0b-9e35-1994c8031ede" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_NorthAmericaMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_fd0ce648-4e1c-4fb8-8d68-7030d7b8919a" xlink:to="loc_srt_NorthAmericaMember_f5fcbc7a-fd3b-4e0b-9e35-1994c8031ede" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EuropeMember_9ef27756-8ead-4d96-87a2-581a677a46fd" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_EuropeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_fd0ce648-4e1c-4fb8-8d68-7030d7b8919a" xlink:to="loc_srt_EuropeMember_9ef27756-8ead-4d96-87a2-581a677a46fd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_OtherGeographicalLocationMember_618d70fd-3e03-4357-81a2-5e280533068e" xlink:href="ftre-20251231.xsd#ftre_OtherGeographicalLocationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_fd0ce648-4e1c-4fb8-8d68-7030d7b8919a" xlink:to="loc_ftre_OtherGeographicalLocationMember_618d70fd-3e03-4357-81a2-5e280533068e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_PropertyPlantAndEquipmentAndOperatingLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization_b063e6f6-0f2a-4508-bf27-5b8b3d4c7dcb" xlink:href="ftre-20251231.xsd#ftre_PropertyPlantAndEquipmentAndOperatingLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_5fbf1e44-6aa5-4ca5-b999-49ac83c5211f" xlink:to="loc_ftre_PropertyPlantAndEquipmentAndOperatingLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization_b063e6f6-0f2a-4508-bf27-5b8b3d4c7dcb" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fortrea.com/role/GOODWILLANDINTANGIBLEASSETSComponentsofIntangibleAssetsDetails" xlink:type="simple" xlink:href="ftre-20251231.xsd#GOODWILLANDINTANGIBLEASSETSComponentsofIntangibleAssetsDetails"/>
  <link:definitionLink xlink:role="http://www.fortrea.com/role/GOODWILLANDINTANGIBLEASSETSComponentsofIntangibleAssetsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_f6fcd60a-b84e-460d-af7a-0c64d61ff1d2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_42d40dd9-2c5c-4959-ada6-a9d13c8d3f36" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_f6fcd60a-b84e-460d-af7a-0c64d61ff1d2" xlink:to="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_42d40dd9-2c5c-4959-ada6-a9d13c8d3f36" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_c3ebcbc2-0cf0-4acd-8bed-b57be04fd80a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfFiniteLivedIntangibleAssetsTable_42d40dd9-2c5c-4959-ada6-a9d13c8d3f36" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_c3ebcbc2-0cf0-4acd-8bed-b57be04fd80a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_c3ebcbc2-0cf0-4acd-8bed-b57be04fd80a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_c3ebcbc2-0cf0-4acd-8bed-b57be04fd80a" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_c3ebcbc2-0cf0-4acd-8bed-b57be04fd80a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_e28dd8f3-32aa-4615-8fe4-1a3515b2fb4e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_c3ebcbc2-0cf0-4acd-8bed-b57be04fd80a" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_e28dd8f3-32aa-4615-8fe4-1a3515b2fb4e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_e1fa7929-a49f-4d23-a1ea-e82334a3bff7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_e28dd8f3-32aa-4615-8fe4-1a3515b2fb4e" xlink:to="loc_us-gaap_CustomerRelationshipsMember_e1fa7929-a49f-4d23-a1ea-e82334a3bff7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TechnologyBasedIntangibleAssetsMember_8fa304fe-2830-4d63-86d8-ac1b40bf00da" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TechnologyBasedIntangibleAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_e28dd8f3-32aa-4615-8fe4-1a3515b2fb4e" xlink:to="loc_us-gaap_TechnologyBasedIntangibleAssetsMember_8fa304fe-2830-4d63-86d8-ac1b40bf00da" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherIntangibleAssetsMember_cba8eeab-3b6b-4895-8b77-a4d7f879fb73" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherIntangibleAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_e28dd8f3-32aa-4615-8fe4-1a3515b2fb4e" xlink:to="loc_us-gaap_OtherIntangibleAssetsMember_cba8eeab-3b6b-4895-8b77-a4d7f879fb73" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_d21ab30d-8376-42b4-bb45-9d0772264fde" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_f6fcd60a-b84e-460d-af7a-0c64d61ff1d2" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_d21ab30d-8376-42b4-bb45-9d0772264fde" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_3ec6f239-46bc-4f99-b8aa-7a663e9f10b2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_f6fcd60a-b84e-460d-af7a-0c64d61ff1d2" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_3ec6f239-46bc-4f99-b8aa-7a663e9f10b2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_3f216499-9392-480d-96d3-2dd847feb992" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_f6fcd60a-b84e-460d-af7a-0c64d61ff1d2" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_3f216499-9392-480d-96d3-2dd847feb992" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fortrea.com/role/DEBTNarrativeDetails" xlink:type="simple" xlink:href="ftre-20251231.xsd#DEBTNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.fortrea.com/role/DEBTNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_985bcded-9012-4941-aab0-4381405bf1b5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_eaa1d746-abe7-4cdc-9b22-32aeb0eed532" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_985bcded-9012-4941-aab0-4381405bf1b5" xlink:to="loc_us-gaap_DebtInstrumentTable_eaa1d746-abe7-4cdc-9b22-32aeb0eed532" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_0a6260db-039c-4837-b727-c02be886531e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_eaa1d746-abe7-4cdc-9b22-32aeb0eed532" xlink:to="loc_us-gaap_CreditFacilityAxis_0a6260db-039c-4837-b727-c02be886531e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_0a6260db-039c-4837-b727-c02be886531e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_0a6260db-039c-4837-b727-c02be886531e" xlink:to="loc_us-gaap_CreditFacilityDomain_0a6260db-039c-4837-b727-c02be886531e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_a6555cef-24b8-47c2-b7e3-147479d122fa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_0a6260db-039c-4837-b727-c02be886531e" xlink:to="loc_us-gaap_CreditFacilityDomain_a6555cef-24b8-47c2-b7e3-147479d122fa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_42b1affe-4d1d-42d2-92c0-b955415dde05" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_a6555cef-24b8-47c2-b7e3-147479d122fa" xlink:to="loc_us-gaap_SecuredDebtMember_42b1affe-4d1d-42d2-92c0-b955415dde05" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_bc1abb2f-ce45-4778-9e75-96488f5e604c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_a6555cef-24b8-47c2-b7e3-147479d122fa" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_bc1abb2f-ce45-4778-9e75-96488f5e604c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BridgeLoanMember_75293cbc-058f-4467-9b26-d7c6e46868a5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BridgeLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_a6555cef-24b8-47c2-b7e3-147479d122fa" xlink:to="loc_us-gaap_BridgeLoanMember_75293cbc-058f-4467-9b26-d7c6e46868a5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LetterOfCreditMember_cec23aec-2768-42d8-912a-a6f1fe30a968" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LetterOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_a6555cef-24b8-47c2-b7e3-147479d122fa" xlink:to="loc_us-gaap_LetterOfCreditMember_cec23aec-2768-42d8-912a-a6f1fe30a968" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_37db6179-50ea-435f-bc6e-254d7a0e6b79" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_eaa1d746-abe7-4cdc-9b22-32aeb0eed532" xlink:to="loc_us-gaap_DebtInstrumentAxis_37db6179-50ea-435f-bc6e-254d7a0e6b79" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_37db6179-50ea-435f-bc6e-254d7a0e6b79_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_37db6179-50ea-435f-bc6e-254d7a0e6b79" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_37db6179-50ea-435f-bc6e-254d7a0e6b79_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_cc824fee-fa63-4cfc-abd8-ce22c10c9fce" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_37db6179-50ea-435f-bc6e-254d7a0e6b79" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_cc824fee-fa63-4cfc-abd8-ce22c10c9fce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_SeniorSecuredTermLoanAFacilityDue2028Member_199532bb-45d2-498b-baad-4a2bd7eddab5" xlink:href="ftre-20251231.xsd#ftre_SeniorSecuredTermLoanAFacilityDue2028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_cc824fee-fa63-4cfc-abd8-ce22c10c9fce" xlink:to="loc_ftre_SeniorSecuredTermLoanAFacilityDue2028Member_199532bb-45d2-498b-baad-4a2bd7eddab5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_SeniorSecuredTermLoanBFacilityDue2030Member_a0557795-da90-4bfd-b00a-8382a832fad6" xlink:href="ftre-20251231.xsd#ftre_SeniorSecuredTermLoanBFacilityDue2030Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_cc824fee-fa63-4cfc-abd8-ce22c10c9fce" xlink:to="loc_ftre_SeniorSecuredTermLoanBFacilityDue2030Member_a0557795-da90-4bfd-b00a-8382a832fad6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_A75SeniorNotesDue2030Member_16887a83-23d4-4d62-a106-7b3fdc98296f" xlink:href="ftre-20251231.xsd#ftre_A75SeniorNotesDue2030Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_cc824fee-fa63-4cfc-abd8-ce22c10c9fce" xlink:to="loc_ftre_A75SeniorNotesDue2030Member_16887a83-23d4-4d62-a106-7b3fdc98296f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_SeniorSecuredRevolvingCreditFacilityMember_27d3cad2-4eb5-4b90-a496-01086b09e62f" xlink:href="ftre-20251231.xsd#ftre_SeniorSecuredRevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_cc824fee-fa63-4cfc-abd8-ce22c10c9fce" xlink:to="loc_ftre_SeniorSecuredRevolvingCreditFacilityMember_27d3cad2-4eb5-4b90-a496-01086b09e62f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_7aa35863-ca01-4c59-a8d8-93c2c481b97b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_eaa1d746-abe7-4cdc-9b22-32aeb0eed532" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_7aa35863-ca01-4c59-a8d8-93c2c481b97b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_7aa35863-ca01-4c59-a8d8-93c2c481b97b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_7aa35863-ca01-4c59-a8d8-93c2c481b97b" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_7aa35863-ca01-4c59-a8d8-93c2c481b97b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_7b9db832-8f04-43f6-a75e-a01619b3ee13" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_7aa35863-ca01-4c59-a8d8-93c2c481b97b" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_7b9db832-8f04-43f6-a75e-a01619b3ee13" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_d046e199-8959-4591-a830-9696e7a41c24" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_7b9db832-8f04-43f6-a75e-a01619b3ee13" xlink:to="loc_us-gaap_LineOfCreditMember_d046e199-8959-4591-a830-9696e7a41c24" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeniorNotesMember_9d89bdd0-e937-432f-98ea-8b283b26b24a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SeniorNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_7b9db832-8f04-43f6-a75e-a01619b3ee13" xlink:to="loc_us-gaap_SeniorNotesMember_9d89bdd0-e937-432f-98ea-8b283b26b24a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019c715a-c21e-7169-bcc4-2f457a16b654" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_eaa1d746-abe7-4cdc-9b22-32aeb0eed532" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019c715a-c21e-7169-bcc4-2f457a16b654" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019c715a-c21e-7169-bcc4-2f457a16b654_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019c715a-c21e-7169-bcc4-2f457a16b654" xlink:to="loc_us-gaap_SegmentDomain_019c715a-c21e-7169-bcc4-2f457a16b654_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019c715a-c21e-7dc6-8161-ec3ed6ca9e18" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019c715a-c21e-7169-bcc4-2f457a16b654" xlink:to="loc_us-gaap_SegmentDomain_019c715a-c21e-7dc6-8161-ec3ed6ca9e18" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_EnablingServicesSegmentMember_019c715a-c21e-7c65-95a7-9aff181d8d7e" xlink:href="ftre-20251231.xsd#ftre_EnablingServicesSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019c715a-c21e-7dc6-8161-ec3ed6ca9e18" xlink:to="loc_ftre_EnablingServicesSegmentMember_019c715a-c21e-7c65-95a7-9aff181d8d7e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_956ca18d-5ae1-4a8e-a1e0-c21e897d4d02" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_985bcded-9012-4941-aab0-4381405bf1b5" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_956ca18d-5ae1-4a8e-a1e0-c21e897d4d02" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_1ec8921e-849b-4381-b1bf-e7b31d7b5ded" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_985bcded-9012-4941-aab0-4381405bf1b5" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_1ec8921e-849b-4381-b1bf-e7b31d7b5ded" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfLongTermDebt_0d09cf34-0707-488f-bd0f-11d2abbbafe7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RepaymentsOfLongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_985bcded-9012-4941-aab0-4381405bf1b5" xlink:to="loc_us-gaap_RepaymentsOfLongTermDebt_0d09cf34-0707-488f-bd0f-11d2abbbafe7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WriteOffOfDeferredDebtIssuanceCost_1b53f443-4b51-44ce-b3d5-f5965d667e22" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_WriteOffOfDeferredDebtIssuanceCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_985bcded-9012-4941-aab0-4381405bf1b5" xlink:to="loc_us-gaap_WriteOffOfDeferredDebtIssuanceCost_1b53f443-4b51-44ce-b3d5-f5965d667e22" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_e35d3c9d-4c97-4a2b-a40e-adbc5fea9a44" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_985bcded-9012-4941-aab0-4381405bf1b5" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_e35d3c9d-4c97-4a2b-a40e-adbc5fea9a44" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfSeniorLongTermDebt_43e60b37-474c-4348-b3c7-909b7b0b7fc2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProceedsFromIssuanceOfSeniorLongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_985bcded-9012-4941-aab0-4381405bf1b5" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfSeniorLongTermDebt_43e60b37-474c-4348-b3c7-909b7b0b7fc2" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_DebtInstrumentRepurchaseAmountFollowingSaleOfAssets_d0894df4-6953-4587-8876-a7762f0eb507" xlink:href="ftre-20251231.xsd#ftre_DebtInstrumentRepurchaseAmountFollowingSaleOfAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_985bcded-9012-4941-aab0-4381405bf1b5" xlink:to="loc_ftre_DebtInstrumentRepurchaseAmountFollowingSaleOfAssets_d0894df4-6953-4587-8876-a7762f0eb507" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTerm_9008cabe-0d6f-4b93-99a2-e24e7e84e9fb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_985bcded-9012-4941-aab0-4381405bf1b5" xlink:to="loc_us-gaap_DebtInstrumentTerm_9008cabe-0d6f-4b93-99a2-e24e7e84e9fb" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfSecuredDebt_24452434-cecf-41f1-89d1-747f7ff7fd38" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProceedsFromIssuanceOfSecuredDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_985bcded-9012-4941-aab0-4381405bf1b5" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfSecuredDebt_24452434-cecf-41f1-89d1-747f7ff7fd38" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityInterestRateAtPeriodEnd_4e103249-e501-49d0-8c42-4ded6bfebe02" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityInterestRateAtPeriodEnd"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_985bcded-9012-4941-aab0-4381405bf1b5" xlink:to="loc_us-gaap_LineOfCreditFacilityInterestRateAtPeriodEnd_4e103249-e501-49d0-8c42-4ded6bfebe02" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCredit_d8c9d214-e468-496b-9ad5-f528114f9380" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_985bcded-9012-4941-aab0-4381405bf1b5" xlink:to="loc_us-gaap_LineOfCredit_d8c9d214-e468-496b-9ad5-f528114f9380" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LettersOfCreditOutstandingAmount_9181776e-6490-4fa5-96e7-2c4ccd64a30d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LettersOfCreditOutstandingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_985bcded-9012-4941-aab0-4381405bf1b5" xlink:to="loc_us-gaap_LettersOfCreditOutstandingAmount_9181776e-6490-4fa5-96e7-2c4ccd64a30d" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_4c1d6610-f68f-4a0a-9cc4-dad5502271cf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_985bcded-9012-4941-aab0-4381405bf1b5" xlink:to="loc_us-gaap_LineOfCreditFacilityRemainingBorrowingCapacity_4c1d6610-f68f-4a0a-9cc4-dad5502271cf" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_LineOfCreditFacilityAnnualAgencyFee_515d247c-1d04-419e-b4a1-6bbaec33b130" xlink:href="ftre-20251231.xsd#ftre_LineOfCreditFacilityAnnualAgencyFee"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_985bcded-9012-4941-aab0-4381405bf1b5" xlink:to="loc_ftre_LineOfCreditFacilityAnnualAgencyFee_515d247c-1d04-419e-b4a1-6bbaec33b130" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityCommitmentFeePercentage_5e8bb551-2568-4000-9a5b-03c3bf70b277" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityCommitmentFeePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_985bcded-9012-4941-aab0-4381405bf1b5" xlink:to="loc_us-gaap_LineOfCreditFacilityCommitmentFeePercentage_5e8bb551-2568-4000-9a5b-03c3bf70b277" xlink:type="arc" order="14"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fortrea.com/role/DEBTScheduleofDebtDetails" xlink:type="simple" xlink:href="ftre-20251231.xsd#DEBTScheduleofDebtDetails"/>
  <link:definitionLink xlink:role="http://www.fortrea.com/role/DEBTScheduleofDebtDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_fedfc94c-e339-419c-9776-85fd53464ee7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_b5be529a-509a-416d-8690-46e4fc2e2fd2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_fedfc94c-e339-419c-9776-85fd53464ee7" xlink:to="loc_us-gaap_DebtInstrumentTable_b5be529a-509a-416d-8690-46e4fc2e2fd2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_650264e5-55e9-4d3a-b796-cc5a1c8338d9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_b5be529a-509a-416d-8690-46e4fc2e2fd2" xlink:to="loc_us-gaap_DebtInstrumentAxis_650264e5-55e9-4d3a-b796-cc5a1c8338d9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_650264e5-55e9-4d3a-b796-cc5a1c8338d9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_650264e5-55e9-4d3a-b796-cc5a1c8338d9" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_650264e5-55e9-4d3a-b796-cc5a1c8338d9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_810cab1c-2780-4033-b93b-fa1333ab56e1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_650264e5-55e9-4d3a-b796-cc5a1c8338d9" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_810cab1c-2780-4033-b93b-fa1333ab56e1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_A75SeniorNotesDue2030Member_c8f9855a-c043-4653-beba-53b5473ab339" xlink:href="ftre-20251231.xsd#ftre_A75SeniorNotesDue2030Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_810cab1c-2780-4033-b93b-fa1333ab56e1" xlink:to="loc_ftre_A75SeniorNotesDue2030Member_c8f9855a-c043-4653-beba-53b5473ab339" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_SeniorSecuredTermLoanAFacilityDue2028Member_5d3884fc-9d60-4bb3-9634-e5454f57b3b7" xlink:href="ftre-20251231.xsd#ftre_SeniorSecuredTermLoanAFacilityDue2028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_810cab1c-2780-4033-b93b-fa1333ab56e1" xlink:to="loc_ftre_SeniorSecuredTermLoanAFacilityDue2028Member_5d3884fc-9d60-4bb3-9634-e5454f57b3b7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_SeniorSecuredTermLoanBFacilityDue2030Member_a094d615-0fac-4c9e-a793-961bd5747145" xlink:href="ftre-20251231.xsd#ftre_SeniorSecuredTermLoanBFacilityDue2030Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_810cab1c-2780-4033-b93b-fa1333ab56e1" xlink:to="loc_ftre_SeniorSecuredTermLoanBFacilityDue2030Member_a094d615-0fac-4c9e-a793-961bd5747145" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_91f79083-393d-48bc-9bef-836e33fa98bf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_b5be529a-509a-416d-8690-46e4fc2e2fd2" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_91f79083-393d-48bc-9bef-836e33fa98bf" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_91f79083-393d-48bc-9bef-836e33fa98bf_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_91f79083-393d-48bc-9bef-836e33fa98bf" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_91f79083-393d-48bc-9bef-836e33fa98bf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_2b487282-2bc4-49bd-b562-ea69f35e2388" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_91f79083-393d-48bc-9bef-836e33fa98bf" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_2b487282-2bc4-49bd-b562-ea69f35e2388" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeniorNotesMember_7f323376-f226-4132-ab0c-ef7fa2019c66" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SeniorNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_2b487282-2bc4-49bd-b562-ea69f35e2388" xlink:to="loc_us-gaap_SeniorNotesMember_7f323376-f226-4132-ab0c-ef7fa2019c66" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_f28b8348-eec8-4711-8bb7-46aa94c97898" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_2b487282-2bc4-49bd-b562-ea69f35e2388" xlink:to="loc_us-gaap_LineOfCreditMember_f28b8348-eec8-4711-8bb7-46aa94c97898" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_ebcc67dd-a10e-46d9-9191-a7fd8207f0ff" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_b5be529a-509a-416d-8690-46e4fc2e2fd2" xlink:to="loc_us-gaap_CreditFacilityAxis_ebcc67dd-a10e-46d9-9191-a7fd8207f0ff" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_ebcc67dd-a10e-46d9-9191-a7fd8207f0ff_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_ebcc67dd-a10e-46d9-9191-a7fd8207f0ff" xlink:to="loc_us-gaap_CreditFacilityDomain_ebcc67dd-a10e-46d9-9191-a7fd8207f0ff_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_f2d3d1ef-309e-4c42-b31a-bd3d152c7a5b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_ebcc67dd-a10e-46d9-9191-a7fd8207f0ff" xlink:to="loc_us-gaap_CreditFacilityDomain_f2d3d1ef-309e-4c42-b31a-bd3d152c7a5b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_6a170332-61a7-477f-b229-0aee5c20013f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_f2d3d1ef-309e-4c42-b31a-bd3d152c7a5b" xlink:to="loc_us-gaap_SecuredDebtMember_6a170332-61a7-477f-b229-0aee5c20013f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermBorrowingsAbstract_dd091590-7a0a-4784-800c-f8ca8f12ea48" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShortTermBorrowingsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_fedfc94c-e339-419c-9776-85fd53464ee7" xlink:to="loc_us-gaap_ShortTermBorrowingsAbstract_dd091590-7a0a-4784-800c-f8ca8f12ea48" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_804b0c51-9db7-49e0-9d48-c2bd3d826b0b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermBorrowingsAbstract_dd091590-7a0a-4784-800c-f8ca8f12ea48" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_804b0c51-9db7-49e0-9d48-c2bd3d826b0b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_DebtInstrumentRepurchaseAmountFollowingSaleOfAssets_060646d5-8ae8-4874-8a8d-1210e3c60f8f" xlink:href="ftre-20251231.xsd#ftre_DebtInstrumentRepurchaseAmountFollowingSaleOfAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermBorrowingsAbstract_dd091590-7a0a-4784-800c-f8ca8f12ea48" xlink:to="loc_ftre_DebtInstrumentRepurchaseAmountFollowingSaleOfAssets_060646d5-8ae8-4874-8a8d-1210e3c60f8f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredFinanceCostsCurrentNet_4be3c6f0-6cd8-4cfa-a5e1-dedc6995e4b1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DeferredFinanceCostsCurrentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermBorrowingsAbstract_dd091590-7a0a-4784-800c-f8ca8f12ea48" xlink:to="loc_us-gaap_DeferredFinanceCostsCurrentNet_4be3c6f0-6cd8-4cfa-a5e1-dedc6995e4b1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtCurrent_d013f5b3-99ac-43aa-a052-25d22226599d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebtCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShortTermBorrowingsAbstract_dd091590-7a0a-4784-800c-f8ca8f12ea48" xlink:to="loc_us-gaap_LongTermDebtCurrent_d013f5b3-99ac-43aa-a052-25d22226599d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtAndCapitalLeaseObligationsAbstract_464aa811-e48a-4e8c-979b-16b3b813eac0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebtAndCapitalLeaseObligationsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_fedfc94c-e339-419c-9776-85fd53464ee7" xlink:to="loc_us-gaap_LongTermDebtAndCapitalLeaseObligationsAbstract_464aa811-e48a-4e8c-979b-16b3b813eac0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_LongTermDebtGrossExcludingCurrentMaturities_16e85d33-e02e-45c2-8f96-67be5b43e246" xlink:href="ftre-20251231.xsd#ftre_LongTermDebtGrossExcludingCurrentMaturities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermDebtAndCapitalLeaseObligationsAbstract_464aa811-e48a-4e8c-979b-16b3b813eac0" xlink:to="loc_ftre_LongTermDebtGrossExcludingCurrentMaturities_16e85d33-e02e-45c2-8f96-67be5b43e246" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredFinanceCostsNoncurrentNet_6760b507-a4ba-4d3b-ae8b-ced9d81503bb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DeferredFinanceCostsNoncurrentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermDebtAndCapitalLeaseObligationsAbstract_464aa811-e48a-4e8c-979b-16b3b813eac0" xlink:to="loc_us-gaap_DeferredFinanceCostsNoncurrentNet_6760b507-a4ba-4d3b-ae8b-ced9d81503bb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtNoncurrent_e94c896f-84ad-4125-b13e-aaf048196066" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebtNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongTermDebtAndCapitalLeaseObligationsAbstract_464aa811-e48a-4e8c-979b-16b3b813eac0" xlink:to="loc_us-gaap_LongTermDebtNoncurrent_e94c896f-84ad-4125-b13e-aaf048196066" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fortrea.com/role/DEBTScheduleofEstimatedFairValueofDebtDetails" xlink:type="simple" xlink:href="ftre-20251231.xsd#DEBTScheduleofEstimatedFairValueofDebtDetails"/>
  <link:definitionLink xlink:role="http://www.fortrea.com/role/DEBTScheduleofEstimatedFairValueofDebtDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_10ad5ce9-7274-47c0-a9e4-59948464538a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_3be07114-2e4a-431d-8501-e73a9b8f6c65" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_10ad5ce9-7274-47c0-a9e4-59948464538a" xlink:to="loc_us-gaap_DebtInstrumentTable_3be07114-2e4a-431d-8501-e73a9b8f6c65" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementBasisAxis_487ae000-4029-4bd5-8edc-4d7f92bc1b52" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByMeasurementBasisAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_3be07114-2e4a-431d-8501-e73a9b8f6c65" xlink:to="loc_us-gaap_FairValueByMeasurementBasisAxis_487ae000-4029-4bd5-8edc-4d7f92bc1b52" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_487ae000-4029-4bd5-8edc-4d7f92bc1b52_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_487ae000-4029-4bd5-8edc-4d7f92bc1b52" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_487ae000-4029-4bd5-8edc-4d7f92bc1b52_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueDisclosureItemAmountsDomain_721630d6-74e5-490a-86e6-2415a67ab37d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueDisclosureItemAmountsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_487ae000-4029-4bd5-8edc-4d7f92bc1b52" xlink:to="loc_us-gaap_FairValueDisclosureItemAmountsDomain_721630d6-74e5-490a-86e6-2415a67ab37d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_bcb46144-2656-44e5-91cd-853c1503ca70" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_721630d6-74e5-490a-86e6-2415a67ab37d" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_bcb46144-2656-44e5-91cd-853c1503ca70" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_b43d15c3-c7a6-467a-853e-99a70e8f3990" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CarryingReportedAmountFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_bcb46144-2656-44e5-91cd-853c1503ca70" xlink:to="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_b43d15c3-c7a6-467a-853e-99a70e8f3990" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_2a9b66a3-cd4f-4dff-b36a-5f4fbcd67139" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_bcb46144-2656-44e5-91cd-853c1503ca70" xlink:to="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_2a9b66a3-cd4f-4dff-b36a-5f4fbcd67139" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_9c8230ac-97a7-4d7e-a9a8-f331f22f19a7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_3be07114-2e4a-431d-8501-e73a9b8f6c65" xlink:to="loc_us-gaap_DebtInstrumentAxis_9c8230ac-97a7-4d7e-a9a8-f331f22f19a7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_9c8230ac-97a7-4d7e-a9a8-f331f22f19a7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_9c8230ac-97a7-4d7e-a9a8-f331f22f19a7" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_9c8230ac-97a7-4d7e-a9a8-f331f22f19a7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_b078ebb9-7216-425e-b696-fc7d0d4f27d4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_9c8230ac-97a7-4d7e-a9a8-f331f22f19a7" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_b078ebb9-7216-425e-b696-fc7d0d4f27d4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_A75SeniorNotesDue2030Member_cb535a83-a0e9-4c2c-b6b5-420e28fbaedc" xlink:href="ftre-20251231.xsd#ftre_A75SeniorNotesDue2030Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_b078ebb9-7216-425e-b696-fc7d0d4f27d4" xlink:to="loc_ftre_A75SeniorNotesDue2030Member_cb535a83-a0e9-4c2c-b6b5-420e28fbaedc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_SeniorSecuredTermLoanAFacilityDue2028Member_cb5fc797-b35d-4216-8422-d7b136d27738" xlink:href="ftre-20251231.xsd#ftre_SeniorSecuredTermLoanAFacilityDue2028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_b078ebb9-7216-425e-b696-fc7d0d4f27d4" xlink:to="loc_ftre_SeniorSecuredTermLoanAFacilityDue2028Member_cb5fc797-b35d-4216-8422-d7b136d27738" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_SeniorSecuredTermLoanBFacilityDue2030Member_78a2fea6-a5e4-489a-85f6-816d19c2bc15" xlink:href="ftre-20251231.xsd#ftre_SeniorSecuredTermLoanBFacilityDue2030Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_b078ebb9-7216-425e-b696-fc7d0d4f27d4" xlink:to="loc_ftre_SeniorSecuredTermLoanBFacilityDue2030Member_78a2fea6-a5e4-489a-85f6-816d19c2bc15" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_f409d4fc-fecf-48d0-af70-72315925bdf7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_3be07114-2e4a-431d-8501-e73a9b8f6c65" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_f409d4fc-fecf-48d0-af70-72315925bdf7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_f409d4fc-fecf-48d0-af70-72315925bdf7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_f409d4fc-fecf-48d0-af70-72315925bdf7" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_f409d4fc-fecf-48d0-af70-72315925bdf7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_261c9adb-5010-4e69-b08e-b32fc789bb1f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_f409d4fc-fecf-48d0-af70-72315925bdf7" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_261c9adb-5010-4e69-b08e-b32fc789bb1f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeniorNotesMember_123d2c5d-e66e-4200-9cd9-6289be2d1c2f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SeniorNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_261c9adb-5010-4e69-b08e-b32fc789bb1f" xlink:to="loc_us-gaap_SeniorNotesMember_123d2c5d-e66e-4200-9cd9-6289be2d1c2f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_ebb1841e-0d23-4539-9c63-2310292aeb67" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_261c9adb-5010-4e69-b08e-b32fc789bb1f" xlink:to="loc_us-gaap_LineOfCreditMember_ebb1841e-0d23-4539-9c63-2310292aeb67" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_fbcfc3b5-6589-4afa-8581-19e3d50ca043" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_3be07114-2e4a-431d-8501-e73a9b8f6c65" xlink:to="loc_us-gaap_CreditFacilityAxis_fbcfc3b5-6589-4afa-8581-19e3d50ca043" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_fbcfc3b5-6589-4afa-8581-19e3d50ca043_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_fbcfc3b5-6589-4afa-8581-19e3d50ca043" xlink:to="loc_us-gaap_CreditFacilityDomain_fbcfc3b5-6589-4afa-8581-19e3d50ca043_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_a9e72568-dc46-494c-9d53-9aa0015cfbf7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_fbcfc3b5-6589-4afa-8581-19e3d50ca043" xlink:to="loc_us-gaap_CreditFacilityDomain_a9e72568-dc46-494c-9d53-9aa0015cfbf7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_8f6ad52d-a745-46f7-b854-e6a6bb757d01" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_a9e72568-dc46-494c-9d53-9aa0015cfbf7" xlink:to="loc_us-gaap_SecuredDebtMember_8f6ad52d-a745-46f7-b854-e6a6bb757d01" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtFairValue_8bf66fb9-f28c-43b1-ba16-b415bbb44899" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebtFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_10ad5ce9-7274-47c0-a9e4-59948464538a" xlink:to="loc_us-gaap_LongTermDebtFairValue_8bf66fb9-f28c-43b1-ba16-b415bbb44899" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fortrea.com/role/DERIVATIVEINSTRUMENTSANDHEDGINGACTIVITIESScheduleofDerivativeInstrumentsDetails" xlink:type="simple" xlink:href="ftre-20251231.xsd#DERIVATIVEINSTRUMENTSANDHEDGINGACTIVITIESScheduleofDerivativeInstrumentsDetails"/>
  <link:definitionLink xlink:role="http://www.fortrea.com/role/DERIVATIVEINSTRUMENTSANDHEDGINGACTIVITIESScheduleofDerivativeInstrumentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_9cbb948a-91df-4ad6-8489-cd1f766644c0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_e6ea4306-cc72-4185-988f-6c32b7205607" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_9cbb948a-91df-4ad6-8489-cd1f766644c0" xlink:to="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_e6ea4306-cc72-4185-988f-6c32b7205607" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationAxis_0570f1cf-6b8d-4b62-9c95-7949e687a059" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BalanceSheetLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_e6ea4306-cc72-4185-988f-6c32b7205607" xlink:to="loc_us-gaap_BalanceSheetLocationAxis_0570f1cf-6b8d-4b62-9c95-7949e687a059" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_0570f1cf-6b8d-4b62-9c95-7949e687a059_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_0570f1cf-6b8d-4b62-9c95-7949e687a059" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_0570f1cf-6b8d-4b62-9c95-7949e687a059_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_966f5754-09d7-48c8-aadc-308a85c13a4e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_0570f1cf-6b8d-4b62-9c95-7949e687a059" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_966f5754-09d7-48c8-aadc-308a85c13a4e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedLiabilitiesMember_16a96de8-b3fc-44bf-9e6a-c70a7d12ccae" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccruedLiabilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_966f5754-09d7-48c8-aadc-308a85c13a4e" xlink:to="loc_us-gaap_AccruedLiabilitiesMember_16a96de8-b3fc-44bf-9e6a-c70a7d12ccae" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesMember_436fafc0-8658-4109-a21e-483dd28ae018" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherLiabilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_966f5754-09d7-48c8-aadc-308a85c13a4e" xlink:to="loc_us-gaap_OtherLiabilitiesMember_436fafc0-8658-4109-a21e-483dd28ae018" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrepaidExpensesAndOtherCurrentAssetsMember_20d4b14c-88bf-4b54-a025-b0b84ffa2506" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PrepaidExpensesAndOtherCurrentAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_966f5754-09d7-48c8-aadc-308a85c13a4e" xlink:to="loc_us-gaap_PrepaidExpensesAndOtherCurrentAssetsMember_20d4b14c-88bf-4b54-a025-b0b84ffa2506" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCurrentLiabilitiesMember_0d102404-ae9e-45a4-8b00-eaed83e5bce2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherCurrentLiabilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_966f5754-09d7-48c8-aadc-308a85c13a4e" xlink:to="loc_us-gaap_OtherCurrentLiabilitiesMember_0d102404-ae9e-45a4-8b00-eaed83e5bce2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_2bc4af47-5feb-4073-bd69-c192440e6adf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_e6ea4306-cc72-4185-988f-6c32b7205607" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_2bc4af47-5feb-4073-bd69-c192440e6adf" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_2bc4af47-5feb-4073-bd69-c192440e6adf_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_2bc4af47-5feb-4073-bd69-c192440e6adf" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_2bc4af47-5feb-4073-bd69-c192440e6adf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_6ccdd601-750e-48d9-8867-0183233534fc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_2bc4af47-5feb-4073-bd69-c192440e6adf" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_6ccdd601-750e-48d9-8867-0183233534fc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_565e7fc1-8068-4388-bcbe-72280165a486" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_6ccdd601-750e-48d9-8867-0183233534fc" xlink:to="loc_us-gaap_InterestRateSwapMember_565e7fc1-8068-4388-bcbe-72280165a486" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignExchangeForwardMember_59097bd4-2881-4357-83ce-d5add6e5516f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ForeignExchangeForwardMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_6ccdd601-750e-48d9-8867-0183233534fc" xlink:to="loc_us-gaap_ForeignExchangeForwardMember_59097bd4-2881-4357-83ce-d5add6e5516f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationAxis_f1dd44f4-d4ed-456e-8854-4bddec690559" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgingDesignationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_e6ea4306-cc72-4185-988f-6c32b7205607" xlink:to="loc_us-gaap_HedgingDesignationAxis_f1dd44f4-d4ed-456e-8854-4bddec690559" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_f1dd44f4-d4ed-456e-8854-4bddec690559_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_HedgingDesignationAxis_f1dd44f4-d4ed-456e-8854-4bddec690559" xlink:to="loc_us-gaap_HedgingDesignationDomain_f1dd44f4-d4ed-456e-8854-4bddec690559_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_504dc02a-f20e-460d-a874-52ca2bc0d4cf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_HedgingDesignationAxis_f1dd44f4-d4ed-456e-8854-4bddec690559" xlink:to="loc_us-gaap_HedgingDesignationDomain_504dc02a-f20e-460d-a874-52ca2bc0d4cf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DesignatedAsHedgingInstrumentMember_1857972c-796e-4e9b-84a9-cf2116fc98eb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DesignatedAsHedgingInstrumentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_504dc02a-f20e-460d-a874-52ca2bc0d4cf" xlink:to="loc_us-gaap_DesignatedAsHedgingInstrumentMember_1857972c-796e-4e9b-84a9-cf2116fc98eb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NondesignatedMember_f5b62abd-6109-4ee3-8f4c-5ba413d4e646" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NondesignatedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_504dc02a-f20e-460d-a874-52ca2bc0d4cf" xlink:to="loc_us-gaap_NondesignatedMember_f5b62abd-6109-4ee3-8f4c-5ba413d4e646" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeAssetNotSubjectToMasterNettingArrangement_2a7424b7-bb61-484f-93d7-fa80cb290c12" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeAssetNotSubjectToMasterNettingArrangement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_9cbb948a-91df-4ad6-8489-cd1f766644c0" xlink:to="loc_us-gaap_DerivativeAssetNotSubjectToMasterNettingArrangement_2a7424b7-bb61-484f-93d7-fa80cb290c12" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLiabilityNotSubjectToMasterNettingArrangement_1b0d60f4-5554-4efc-b629-b198fbf68b46" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeLiabilityNotSubjectToMasterNettingArrangement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_9cbb948a-91df-4ad6-8489-cd1f766644c0" xlink:to="loc_us-gaap_DerivativeLiabilityNotSubjectToMasterNettingArrangement_1b0d60f4-5554-4efc-b629-b198fbf68b46" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fortrea.com/role/DERIVATIVEINSTRUMENTSANDHEDGINGACTIVITIESNarrativeDetails" xlink:type="simple" xlink:href="ftre-20251231.xsd#DERIVATIVEINSTRUMENTSANDHEDGINGACTIVITIESNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.fortrea.com/role/DERIVATIVEINSTRUMENTSANDHEDGINGACTIVITIESNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_194ed38e-81ac-4a2f-8f57-74afcbf6c5e4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_f3dbae31-28c5-4ace-9f3d-8fb83b23c907" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_194ed38e-81ac-4a2f-8f57-74afcbf6c5e4" xlink:to="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_f3dbae31-28c5-4ace-9f3d-8fb83b23c907" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_59a3c04b-f18a-465b-bb51-935933b1a72c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_f3dbae31-28c5-4ace-9f3d-8fb83b23c907" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_59a3c04b-f18a-465b-bb51-935933b1a72c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_59a3c04b-f18a-465b-bb51-935933b1a72c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_59a3c04b-f18a-465b-bb51-935933b1a72c" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_59a3c04b-f18a-465b-bb51-935933b1a72c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_7c57b593-3e73-42c0-8396-9945d96e10b6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_59a3c04b-f18a-465b-bb51-935933b1a72c" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_7c57b593-3e73-42c0-8396-9945d96e10b6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_179615dc-a809-49ae-9cef-3489081247e1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_7c57b593-3e73-42c0-8396-9945d96e10b6" xlink:to="loc_us-gaap_InterestRateSwapMember_179615dc-a809-49ae-9cef-3489081247e1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignExchangeForwardMember_05f91370-04ce-4347-95b3-5ed7c4a1735e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ForeignExchangeForwardMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_7c57b593-3e73-42c0-8396-9945d96e10b6" xlink:to="loc_us-gaap_ForeignExchangeForwardMember_05f91370-04ce-4347-95b3-5ed7c4a1735e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationAxis_0289cfdb-7e7e-4149-915b-f89338289c9e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgingDesignationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_f3dbae31-28c5-4ace-9f3d-8fb83b23c907" xlink:to="loc_us-gaap_HedgingDesignationAxis_0289cfdb-7e7e-4149-915b-f89338289c9e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_0289cfdb-7e7e-4149-915b-f89338289c9e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_HedgingDesignationAxis_0289cfdb-7e7e-4149-915b-f89338289c9e" xlink:to="loc_us-gaap_HedgingDesignationDomain_0289cfdb-7e7e-4149-915b-f89338289c9e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_HedgingDesignationDomain_b9719857-0682-46dc-8e6d-1aa9513b4109" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_HedgingDesignationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_HedgingDesignationAxis_0289cfdb-7e7e-4149-915b-f89338289c9e" xlink:to="loc_us-gaap_HedgingDesignationDomain_b9719857-0682-46dc-8e6d-1aa9513b4109" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DesignatedAsHedgingInstrumentMember_d507e23c-f151-4b04-a593-2fce5256ce8b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DesignatedAsHedgingInstrumentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_b9719857-0682-46dc-8e6d-1aa9513b4109" xlink:to="loc_us-gaap_DesignatedAsHedgingInstrumentMember_d507e23c-f151-4b04-a593-2fce5256ce8b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NondesignatedMember_61288060-8070-47f6-ade3-7d709f27c54c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NondesignatedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_HedgingDesignationDomain_b9719857-0682-46dc-8e6d-1aa9513b4109" xlink:to="loc_us-gaap_NondesignatedMember_61288060-8070-47f6-ade3-7d709f27c54c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeNumberOfInstrumentsHeld_bf0c6caf-37a4-46d7-a3db-58a63389dea7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeNumberOfInstrumentsHeld"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_194ed38e-81ac-4a2f-8f57-74afcbf6c5e4" xlink:to="loc_us-gaap_DerivativeNumberOfInstrumentsHeld_bf0c6caf-37a4-46d7-a3db-58a63389dea7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeNotionalAmount_65d9f2d7-11d8-4b92-a5b8-0ec5d960986c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeNotionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_194ed38e-81ac-4a2f-8f57-74afcbf6c5e4" xlink:to="loc_us-gaap_DerivativeNotionalAmount_65d9f2d7-11d8-4b92-a5b8-0ec5d960986c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFixedInterestRate_fd916746-d79b-4d46-8e19-fdb399934f1c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeFixedInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_194ed38e-81ac-4a2f-8f57-74afcbf6c5e4" xlink:to="loc_us-gaap_DerivativeFixedInterestRate_fd916746-d79b-4d46-8e19-fdb399934f1c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateCashFlowHedgeGainLossToBeReclassifiedDuringNext12MonthsNet_ae6774a3-179d-41d0-96fa-051ba2dc0164" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestRateCashFlowHedgeGainLossToBeReclassifiedDuringNext12MonthsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_194ed38e-81ac-4a2f-8f57-74afcbf6c5e4" xlink:to="loc_us-gaap_InterestRateCashFlowHedgeGainLossToBeReclassifiedDuringNext12MonthsNet_ae6774a3-179d-41d0-96fa-051ba2dc0164" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fortrea.com/role/DERIVATIVEINSTRUMENTSANDHEDGINGACTIVITIESPretaxEffectsofCashFlowHedgesDetails" xlink:type="simple" xlink:href="ftre-20251231.xsd#DERIVATIVEINSTRUMENTSANDHEDGINGACTIVITIESPretaxEffectsofCashFlowHedgesDetails"/>
  <link:definitionLink xlink:role="http://www.fortrea.com/role/DERIVATIVEINSTRUMENTSANDHEDGINGACTIVITIESPretaxEffectsofCashFlowHedgesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_d45d26ba-75f2-4ef8-bc49-21d93a473315" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_7f7f71a9-a346-443b-a05e-3cfa00df1fbc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_d45d26ba-75f2-4ef8-bc49-21d93a473315" xlink:to="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_7f7f71a9-a346-443b-a05e-3cfa00df1fbc" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_5d273465-046d-4fee-8d30-84fa3f873dea" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_7f7f71a9-a346-443b-a05e-3cfa00df1fbc" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_5d273465-046d-4fee-8d30-84fa3f873dea" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_5d273465-046d-4fee-8d30-84fa3f873dea_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_5d273465-046d-4fee-8d30-84fa3f873dea" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_5d273465-046d-4fee-8d30-84fa3f873dea_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_4458fdd0-79e9-499d-a7ff-69c70ef2c2fe" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_5d273465-046d-4fee-8d30-84fa3f873dea" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_4458fdd0-79e9-499d-a7ff-69c70ef2c2fe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_83fce64b-c921-4c92-a310-bf3d83dd666b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_4458fdd0-79e9-499d-a7ff-69c70ef2c2fe" xlink:to="loc_us-gaap_InterestRateSwapMember_83fce64b-c921-4c92-a310-bf3d83dd666b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAndTax_e282d35a-e11f-4d4f-842a-a34c9ef547b6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAndTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_d45d26ba-75f2-4ef8-bc49-21d93a473315" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossBeforeReclassificationAndTax_e282d35a-e11f-4d4f-842a-a34c9ef547b6" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fortrea.com/role/DERIVATIVEINSTRUMENTSANDHEDGINGACTIVITIESReclassifiedfromOtherComprehensiveLossintoEarningsDetails" xlink:type="simple" xlink:href="ftre-20251231.xsd#DERIVATIVEINSTRUMENTSANDHEDGINGACTIVITIESReclassifiedfromOtherComprehensiveLossintoEarningsDetails"/>
  <link:definitionLink xlink:role="http://www.fortrea.com/role/DERIVATIVEINSTRUMENTSANDHEDGINGACTIVITIESReclassifiedfromOtherComprehensiveLossintoEarningsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_a5f4d801-694e-406f-be97-070d51efa455" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_92e3d8c1-67d8-48b5-9cc9-8c7f5d94bd10" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_a5f4d801-694e-406f-be97-070d51efa455" xlink:to="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_92e3d8c1-67d8-48b5-9cc9-8c7f5d94bd10" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_b8254851-861c-4948-bbfc-87e22152e020" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_92e3d8c1-67d8-48b5-9cc9-8c7f5d94bd10" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_b8254851-861c-4948-bbfc-87e22152e020" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_b8254851-861c-4948-bbfc-87e22152e020_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_b8254851-861c-4948-bbfc-87e22152e020" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_b8254851-861c-4948-bbfc-87e22152e020_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_68bcfa72-0cc8-40f1-bcc8-c404f86b476e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_b8254851-861c-4948-bbfc-87e22152e020" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_68bcfa72-0cc8-40f1-bcc8-c404f86b476e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateSwapMember_09ab4c3e-6f27-4c60-941b-7da1085a8083" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestRateSwapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_68bcfa72-0cc8-40f1-bcc8-c404f86b476e" xlink:to="loc_us-gaap_InterestRateSwapMember_09ab4c3e-6f27-4c60-941b-7da1085a8083" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_b9474db3-772a-4a75-9dbd-e9ca6a05fe72" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_92e3d8c1-67d8-48b5-9cc9-8c7f5d94bd10" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_b9474db3-772a-4a75-9dbd-e9ca6a05fe72" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_b9474db3-772a-4a75-9dbd-e9ca6a05fe72_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_b9474db3-772a-4a75-9dbd-e9ca6a05fe72" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_b9474db3-772a-4a75-9dbd-e9ca6a05fe72_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_9f84b425-5265-4ecc-8eee-91ff87700b31" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_b9474db3-772a-4a75-9dbd-e9ca6a05fe72" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_9f84b425-5265-4ecc-8eee-91ff87700b31" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseMember_60567466-808a-4786-8787-3bc0de8e1b2b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_9f84b425-5265-4ecc-8eee-91ff87700b31" xlink:to="loc_us-gaap_InterestExpenseMember_60567466-808a-4786-8787-3bc0de8e1b2b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationBeforeTax_65499898-7b28-4ddd-98c9-880eabe587e9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_a5f4d801-694e-406f-be97-070d51efa455" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossCashFlowHedgeGainLossReclassificationBeforeTax_65499898-7b28-4ddd-98c9-880eabe587e9" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fortrea.com/role/DERIVATIVEINSTRUMENTSANDHEDGINGACTIVITIESGainLossforDerivativeContractsNotDesignatedasHedgesDetails" xlink:type="simple" xlink:href="ftre-20251231.xsd#DERIVATIVEINSTRUMENTSANDHEDGINGACTIVITIESGainLossforDerivativeContractsNotDesignatedasHedgesDetails"/>
  <link:definitionLink xlink:role="http://www.fortrea.com/role/DERIVATIVEINSTRUMENTSANDHEDGINGACTIVITIESGainLossforDerivativeContractsNotDesignatedasHedgesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_839239da-6096-4b9a-87df-15ee9ef26e28" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_542abaff-c0da-447b-8492-a83244414c9b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_839239da-6096-4b9a-87df-15ee9ef26e28" xlink:to="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_542abaff-c0da-447b-8492-a83244414c9b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_f1967b4c-f07e-4249-a80f-9dae9b4c1cd3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_542abaff-c0da-447b-8492-a83244414c9b" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_f1967b4c-f07e-4249-a80f-9dae9b4c1cd3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_f1967b4c-f07e-4249-a80f-9dae9b4c1cd3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_f1967b4c-f07e-4249-a80f-9dae9b4c1cd3" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_f1967b4c-f07e-4249-a80f-9dae9b4c1cd3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_8fd36a6a-e430-4ab8-abf3-52aef3fdb365" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_f1967b4c-f07e-4249-a80f-9dae9b4c1cd3" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_8fd36a6a-e430-4ab8-abf3-52aef3fdb365" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignExchangeContractMember_12d215b3-0228-4d1c-aec0-c9818174aef4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ForeignExchangeContractMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_8fd36a6a-e430-4ab8-abf3-52aef3fdb365" xlink:to="loc_us-gaap_ForeignExchangeContractMember_12d215b3-0228-4d1c-aec0-c9818174aef4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_51b7e978-77b3-4ba9-a038-b3105cce5a1f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresTable_542abaff-c0da-447b-8492-a83244414c9b" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_51b7e978-77b3-4ba9-a038-b3105cce5a1f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_51b7e978-77b3-4ba9-a038-b3105cce5a1f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_51b7e978-77b3-4ba9-a038-b3105cce5a1f" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_51b7e978-77b3-4ba9-a038-b3105cce5a1f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_ef79d26c-4d7b-4fad-b357-1f652a192b38" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_51b7e978-77b3-4ba9-a038-b3105cce5a1f" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_ef79d26c-4d7b-4fad-b357-1f652a192b38" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignCurrencyGainLossMember_405eca11-ef78-46b2-a022-cd5f546e4986" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ForeignCurrencyGainLossMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_ef79d26c-4d7b-4fad-b357-1f652a192b38" xlink:to="loc_us-gaap_ForeignCurrencyGainLossMember_405eca11-ef78-46b2-a022-cd5f546e4986" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet_3d1db6b7-81da-4f80-ace7-729af34dc4c6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeInstrumentsAndHedgingActivitiesDisclosuresLineItems_839239da-6096-4b9a-87df-15ee9ef26e28" xlink:to="loc_us-gaap_DerivativeInstrumentsNotDesignatedAsHedgingInstrumentsGainLossNet_3d1db6b7-81da-4f80-ace7-729af34dc4c6" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fortrea.com/role/INCOMETAXESScheduleOfIncomeTaxesPaidNetofRefundsDetails" xlink:type="simple" xlink:href="ftre-20251231.xsd#INCOMETAXESScheduleOfIncomeTaxesPaidNetofRefundsDetails"/>
  <link:definitionLink xlink:role="http://www.fortrea.com/role/INCOMETAXESScheduleOfIncomeTaxesPaidNetofRefundsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationLineItems_019b4a16-f941-73e4-a09d-2090082c2420" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationTable_019b4a16-f941-7178-ae52-e57778297ac9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateReconciliationLineItems_019b4a16-f941-73e4-a09d-2090082c2420" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationTable_019b4a16-f941-7178-ae52-e57778297ac9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityAxis_019b4a16-f941-74c3-9e58-4a4c337aa9c5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxAuthorityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateReconciliationTable_019b4a16-f941-7178-ae52-e57778297ac9" xlink:to="loc_us-gaap_IncomeTaxAuthorityAxis_019b4a16-f941-74c3-9e58-4a4c337aa9c5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_019b4a16-f941-74c3-9e58-4a4c337aa9c5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxAuthorityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_019b4a16-f941-74c3-9e58-4a4c337aa9c5" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_019b4a16-f941-74c3-9e58-4a4c337aa9c5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_019b4a16-f941-722d-9ba1-46605f5bb5b0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxAuthorityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_019b4a16-f941-74c3-9e58-4a4c337aa9c5" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_019b4a16-f941-722d-9ba1-46605f5bb5b0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StateAndLocalJurisdictionMember_019b4a17-3f27-7555-8efa-ff693bd459d9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StateAndLocalJurisdictionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_019b4a16-f941-722d-9ba1-46605f5bb5b0" xlink:to="loc_us-gaap_StateAndLocalJurisdictionMember_019b4a17-3f27-7555-8efa-ff693bd459d9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_stpr_CA_019c6e72-338c-7393-befa-738ddee85fb4" xlink:href="https://xbrl.sec.gov/stpr/2025/stpr-2025.xsd#stpr_CA"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StateAndLocalJurisdictionMember_019b4a17-3f27-7555-8efa-ff693bd459d9" xlink:to="loc_stpr_CA_019c6e72-338c-7393-befa-738ddee85fb4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StateAndLocalTaxJurisdictionOtherMember_019bafe8-82cd-7e12-b4bb-3bd7a962c432" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StateAndLocalTaxJurisdictionOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StateAndLocalJurisdictionMember_019b4a17-3f27-7555-8efa-ff693bd459d9" xlink:to="loc_us-gaap_StateAndLocalTaxJurisdictionOtherMember_019bafe8-82cd-7e12-b4bb-3bd7a962c432" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignCountryMember_019b4a17-d366-7916-80d5-24673cf25c78" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ForeignCountryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_019b4a16-f941-722d-9ba1-46605f5bb5b0" xlink:to="loc_us-gaap_ForeignCountryMember_019b4a17-d366-7916-80d5-24673cf25c78" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_AU_019b8bba-cb64-7ea9-bec9-19d9a412e733" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_AU"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ForeignCountryMember_019b4a17-d366-7916-80d5-24673cf25c78" xlink:to="loc_country_AU_019b8bba-cb64-7ea9-bec9-19d9a412e733" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_BE_019b8bbb-08e0-7784-abfd-1d1ffd17736e" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_BE"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ForeignCountryMember_019b4a17-d366-7916-80d5-24673cf25c78" xlink:to="loc_country_BE_019b8bbb-08e0-7784-abfd-1d1ffd17736e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_BR_019b8bbb-436e-70a6-93cc-3a7a97a31608" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_BR"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ForeignCountryMember_019b4a17-d366-7916-80d5-24673cf25c78" xlink:to="loc_country_BR_019b8bbb-436e-70a6-93cc-3a7a97a31608" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_CA_019b4a16-f941-742f-ab5f-0cbc9aa4b4b0" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_CA"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ForeignCountryMember_019b4a17-d366-7916-80d5-24673cf25c78" xlink:to="loc_country_CA_019b4a16-f941-742f-ab5f-0cbc9aa4b4b0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_CN_019b4a16-f941-7a32-883e-004ee197c7ff" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_CN"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ForeignCountryMember_019b4a17-d366-7916-80d5-24673cf25c78" xlink:to="loc_country_CN_019b4a16-f941-7a32-883e-004ee197c7ff" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_DE_019b4a16-f941-7e8a-91de-c2ea9800da84" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_DE"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ForeignCountryMember_019b4a17-d366-7916-80d5-24673cf25c78" xlink:to="loc_country_DE_019b4a16-f941-7e8a-91de-c2ea9800da84" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_IN_019b4a16-f941-762a-b1ec-3ab9d965cb35" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_IN"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ForeignCountryMember_019b4a17-d366-7916-80d5-24673cf25c78" xlink:to="loc_country_IN_019b4a16-f941-762a-b1ec-3ab9d965cb35" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_IE_019b4a16-f941-7405-97be-b016672ec435" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_IE"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ForeignCountryMember_019b4a17-d366-7916-80d5-24673cf25c78" xlink:to="loc_country_IE_019b4a16-f941-7405-97be-b016672ec435" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_IT_019b4a16-f941-7cdd-b075-5e5dcc69af48" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_IT"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ForeignCountryMember_019b4a17-d366-7916-80d5-24673cf25c78" xlink:to="loc_country_IT_019b4a16-f941-7cdd-b075-5e5dcc69af48" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_ES_019c35a9-af8d-70b9-981d-e0dc93acb5fd" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_ES"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ForeignCountryMember_019b4a17-d366-7916-80d5-24673cf25c78" xlink:to="loc_country_ES_019c35a9-af8d-70b9-981d-e0dc93acb5fd" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignTaxJurisdictionOtherMember_019b4a16-f941-7ba1-bb05-652a4e4c579c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ForeignTaxJurisdictionOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ForeignCountryMember_019b4a17-d366-7916-80d5-24673cf25c78" xlink:to="loc_us-gaap_ForeignTaxJurisdictionOtherMember_019b4a16-f941-7ba1-bb05-652a4e4c579c" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxPaidFederalAfterRefundReceived_019b4a16-f941-74e2-a53d-03705f8717e3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxPaidFederalAfterRefundReceived"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateReconciliationLineItems_019b4a16-f941-73e4-a09d-2090082c2420" xlink:to="loc_us-gaap_IncomeTaxPaidFederalAfterRefundReceived_019b4a16-f941-74e2-a53d-03705f8717e3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxPaidStateAndLocalAfterRefundReceived_019b4a16-f941-7381-9d8d-4984b11ff6c5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxPaidStateAndLocalAfterRefundReceived"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateReconciliationLineItems_019b4a16-f941-73e4-a09d-2090082c2420" xlink:to="loc_us-gaap_IncomeTaxPaidStateAndLocalAfterRefundReceived_019b4a16-f941-7381-9d8d-4984b11ff6c5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxPaidForeignAfterRefundReceived_019b4a16-f941-7911-9b1d-8eb990c9fddf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxPaidForeignAfterRefundReceived"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateReconciliationLineItems_019b4a16-f941-73e4-a09d-2090082c2420" xlink:to="loc_us-gaap_IncomeTaxPaidForeignAfterRefundReceived_019b4a16-f941-7911-9b1d-8eb990c9fddf" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxesPaidNet_019b4a16-f941-7971-9f7f-3f7f0c7aba93" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxesPaidNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateReconciliationLineItems_019b4a16-f941-73e4-a09d-2090082c2420" xlink:to="loc_us-gaap_IncomeTaxesPaidNet_019b4a16-f941-7971-9f7f-3f7f0c7aba93" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fortrea.com/role/INCOMETAXESScheduleofEffectiveIncomeTaxRateReconciliationDetails" xlink:type="simple" xlink:href="ftre-20251231.xsd#INCOMETAXESScheduleofEffectiveIncomeTaxRateReconciliationDetails"/>
  <link:definitionLink xlink:role="http://www.fortrea.com/role/INCOMETAXESScheduleofEffectiveIncomeTaxRateReconciliationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationLineItems_019b4a29-5121-7cf9-8e25-aaefbef31117" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationTable_019b4a29-5121-7857-b4fb-cdfee90bb6a3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateReconciliationLineItems_019b4a29-5121-7cf9-8e25-aaefbef31117" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationTable_019b4a29-5121-7857-b4fb-cdfee90bb6a3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityAxis_019b4a29-5121-7a63-8348-0ba13093e634" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxAuthorityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateReconciliationTable_019b4a29-5121-7857-b4fb-cdfee90bb6a3" xlink:to="loc_us-gaap_IncomeTaxAuthorityAxis_019b4a29-5121-7a63-8348-0ba13093e634" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_019b4a29-5121-7a63-8348-0ba13093e634_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxAuthorityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_019b4a29-5121-7a63-8348-0ba13093e634" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_019b4a29-5121-7a63-8348-0ba13093e634_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_019b4a29-5121-7968-82cf-00d4880e5a26" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxAuthorityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_019b4a29-5121-7a63-8348-0ba13093e634" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_019b4a29-5121-7968-82cf-00d4880e5a26" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignCountryMember_019b4a34-4bfd-7c85-8018-707ccfa226f5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ForeignCountryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_019b4a29-5121-7968-82cf-00d4880e5a26" xlink:to="loc_us-gaap_ForeignCountryMember_019b4a34-4bfd-7c85-8018-707ccfa226f5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_GB_019b4a29-5121-738a-9ca4-bf7a875197b4" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_GB"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ForeignCountryMember_019b4a34-4bfd-7c85-8018-707ccfa226f5" xlink:to="loc_country_GB_019b4a29-5121-738a-9ca4-bf7a875197b4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignTaxJurisdictionOtherMember_019b4a29-5121-7f77-8978-2176c571e518" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ForeignTaxJurisdictionOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ForeignCountryMember_019b4a34-4bfd-7c85-8018-707ccfa226f5" xlink:to="loc_us-gaap_ForeignTaxJurisdictionOtherMember_019b4a29-5121-7f77-8978-2176c571e518" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DomesticCountryMember_019c8c14-958b-7038-a08c-80f887fb7b8f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DomesticCountryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_019b4a29-5121-7968-82cf-00d4880e5a26" xlink:to="loc_us-gaap_DomesticCountryMember_019c8c14-958b-7038-a08c-80f887fb7b8f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_US_019c8c14-72c5-7019-b182-59ca215ff8d3" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_US"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DomesticCountryMember_019c8c14-958b-7038-a08c-80f887fb7b8f" xlink:to="loc_country_US_019c8c14-72c5-7019-b182-59ca215ff8d3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefitContinuingOperationsIncomeTaxReconciliationAbstract_019b4a29-18e8-7d5c-acb6-0eaf85f23e2b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxExpenseBenefitContinuingOperationsIncomeTaxReconciliationAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateReconciliationLineItems_019b4a29-5121-7cf9-8e25-aaefbef31117" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefitContinuingOperationsIncomeTaxReconciliationAbstract_019b4a29-18e8-7d5c-acb6-0eaf85f23e2b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate_019b4a29-5121-721d-9024-0bb8795ed2ea" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxExpenseBenefitContinuingOperationsIncomeTaxReconciliationAbstract_019b4a29-18e8-7d5c-acb6-0eaf85f23e2b" xlink:to="loc_us-gaap_IncomeTaxReconciliationIncomeTaxExpenseBenefitAtFederalStatutoryIncomeTaxRate_019b4a29-5121-721d-9024-0bb8795ed2ea" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationCrossBorderTaxEffectAmount_019b4a29-5121-731c-89d6-e6c6687cdcc8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationCrossBorderTaxEffectAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxExpenseBenefitContinuingOperationsIncomeTaxReconciliationAbstract_019b4a29-18e8-7d5c-acb6-0eaf85f23e2b" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationCrossBorderTaxEffectAmount_019b4a29-5121-731c-89d6-e6c6687cdcc8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxReconciliationTaxCredits_019b4a29-5121-7b63-a94f-a6dece3cd9b2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxReconciliationTaxCredits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxExpenseBenefitContinuingOperationsIncomeTaxReconciliationAbstract_019b4a29-18e8-7d5c-acb6-0eaf85f23e2b" xlink:to="loc_us-gaap_IncomeTaxReconciliationTaxCredits_019b4a29-5121-7b63-a94f-a6dece3cd9b2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxReconciliationNondeductibleExpenseImpairmentLosses_019b4a29-5121-7db5-8680-f91cdc3e534f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxReconciliationNondeductibleExpenseImpairmentLosses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxExpenseBenefitContinuingOperationsIncomeTaxReconciliationAbstract_019b4a29-18e8-7d5c-acb6-0eaf85f23e2b" xlink:to="loc_us-gaap_IncomeTaxReconciliationNondeductibleExpenseImpairmentLosses_019b4a29-5121-7db5-8680-f91cdc3e534f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxReconciliationNondeductibleExpenseOther_019b4a29-5121-7165-8ee3-a90749c69a80" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxReconciliationNondeductibleExpenseOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxExpenseBenefitContinuingOperationsIncomeTaxReconciliationAbstract_019b4a29-18e8-7d5c-acb6-0eaf85f23e2b" xlink:to="loc_us-gaap_IncomeTaxReconciliationNondeductibleExpenseOther_019b4a29-5121-7165-8ee3-a90749c69a80" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxReconciliationChangeInDeferredTaxAssetsValuationAllowance_019b4a29-5121-7322-8c2b-7be01cf5dc57" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxReconciliationChangeInDeferredTaxAssetsValuationAllowance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxExpenseBenefitContinuingOperationsIncomeTaxReconciliationAbstract_019b4a29-18e8-7d5c-acb6-0eaf85f23e2b" xlink:to="loc_us-gaap_IncomeTaxReconciliationChangeInDeferredTaxAssetsValuationAllowance_019b4a29-5121-7322-8c2b-7be01cf5dc57" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxReconciliationOtherAdjustments_019c8c1c-811e-79dd-b339-cc18aaaed64d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxReconciliationOtherAdjustments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxExpenseBenefitContinuingOperationsIncomeTaxReconciliationAbstract_019b4a29-18e8-7d5c-acb6-0eaf85f23e2b" xlink:to="loc_us-gaap_IncomeTaxReconciliationOtherAdjustments_019c8c1c-811e-79dd-b339-cc18aaaed64d" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxReconciliationStateAndLocalIncomeTaxes_019b4a29-5121-75e7-aaf6-f28073d2b599" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxReconciliationStateAndLocalIncomeTaxes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxExpenseBenefitContinuingOperationsIncomeTaxReconciliationAbstract_019b4a29-18e8-7d5c-acb6-0eaf85f23e2b" xlink:to="loc_us-gaap_IncomeTaxReconciliationStateAndLocalIncomeTaxes_019b4a29-5121-75e7-aaf6-f28073d2b599" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxReconciliationForeignIncomeTaxRateDifferential_019b4a29-5121-7f3e-9289-03a690e2f168" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxReconciliationForeignIncomeTaxRateDifferential"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxExpenseBenefitContinuingOperationsIncomeTaxReconciliationAbstract_019b4a29-18e8-7d5c-acb6-0eaf85f23e2b" xlink:to="loc_us-gaap_IncomeTaxReconciliationForeignIncomeTaxRateDifferential_019b4a29-5121-7f3e-9289-03a690e2f168" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxReconciliationTaxContingencies_019b4a29-5121-796f-b069-d5a2aeee82ca" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxReconciliationTaxContingencies"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxExpenseBenefitContinuingOperationsIncomeTaxReconciliationAbstract_019b4a29-18e8-7d5c-acb6-0eaf85f23e2b" xlink:to="loc_us-gaap_IncomeTaxReconciliationTaxContingencies_019b4a29-5121-796f-b069-d5a2aeee82ca" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_019b4a29-5121-7eab-a74c-9bbcbfacdafc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxExpenseBenefitContinuingOperationsIncomeTaxReconciliationAbstract_019b4a29-18e8-7d5c-acb6-0eaf85f23e2b" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_019b4a29-5121-7eab-a74c-9bbcbfacdafc" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract_019b4a21-d573-7e39-94ea-143923f5f161" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateReconciliationLineItems_019b4a29-5121-7cf9-8e25-aaefbef31117" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract_019b4a21-d573-7e39-94ea-143923f5f161" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate_07bea7d2-19b8-46d7-84ac-a55e15ddb691" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract_019b4a21-d573-7e39-94ea-143923f5f161" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationAtFederalStatutoryIncomeTaxRate_07bea7d2-19b8-46d7-84ac-a55e15ddb691" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationCrossBorderTaxEffectPercent_019b4a36-2af6-780d-a3f7-c890d37a9447" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationCrossBorderTaxEffectPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract_019b4a21-d573-7e39-94ea-143923f5f161" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationCrossBorderTaxEffectPercent_019b4a36-2af6-780d-a3f7-c890d37a9447" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes_3abfebd8-b6c1-480a-9437-bd6555186809" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract_019b4a21-d573-7e39-94ea-143923f5f161" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationStateAndLocalIncomeTaxes_3abfebd8-b6c1-480a-9437-bd6555186809" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationForeignIncomeTaxRateDifferential_f8cc6d9b-9d17-4a8a-a372-2ac0c7cb2f0d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationForeignIncomeTaxRateDifferential"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract_019b4a21-d573-7e39-94ea-143923f5f161" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationForeignIncomeTaxRateDifferential_f8cc6d9b-9d17-4a8a-a372-2ac0c7cb2f0d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationTaxCredits_019b4a36-2af6-7a13-a962-3a1ab3b4e680" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationTaxCredits"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract_019b4a21-d573-7e39-94ea-143923f5f161" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationTaxCredits_019b4a36-2af6-7a13-a962-3a1ab3b4e680" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseImpairmentLosses_019b4a36-2af6-74d9-b011-450b81ecc672" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseImpairmentLosses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract_019b4a21-d573-7e39-94ea-143923f5f161" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseImpairmentLosses_019b4a36-2af6-74d9-b011-450b81ecc672" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseOther_335ffb88-a603-49f4-a140-72bc703ef8db" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseOther"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract_019b4a21-d573-7e39-94ea-143923f5f161" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseOther_335ffb88-a603-49f4-a140-72bc703ef8db" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationChangeInDeferredTaxAssetsValuationAllowance_4b9e07a5-9dfe-48b3-acdc-dadc840dea4c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationChangeInDeferredTaxAssetsValuationAllowance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract_019b4a21-d573-7e39-94ea-143923f5f161" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationChangeInDeferredTaxAssetsValuationAllowance_4b9e07a5-9dfe-48b3-acdc-dadc840dea4c" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseShareBasedCompensationCost_5514d408-4330-4c20-af03-072d7fe6bebc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseShareBasedCompensationCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract_019b4a21-d573-7e39-94ea-143923f5f161" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationNondeductibleExpenseShareBasedCompensationCost_5514d408-4330-4c20-af03-072d7fe6bebc" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationChangeInEnactedTaxRate_78d87ff8-defd-424d-863b-ef4c6d9cff3e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationChangeInEnactedTaxRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract_019b4a21-d573-7e39-94ea-143923f5f161" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationChangeInEnactedTaxRate_78d87ff8-defd-424d-863b-ef4c6d9cff3e" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_EffectiveIncomeTaxRateReconciliationInternationalIncomeInclusionsPercent_2f9846dc-4ec1-4d69-82d4-5ef2aa1b3f0a" xlink:href="ftre-20251231.xsd#ftre_EffectiveIncomeTaxRateReconciliationInternationalIncomeInclusionsPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract_019b4a21-d573-7e39-94ea-143923f5f161" xlink:to="loc_ftre_EffectiveIncomeTaxRateReconciliationInternationalIncomeInclusionsPercent_2f9846dc-4ec1-4d69-82d4-5ef2aa1b3f0a" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationOtherAdjustments_019c8c1c-a77a-7f50-96bc-45fb106ae824" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationOtherAdjustments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract_019b4a21-d573-7e39-94ea-143923f5f161" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationOtherAdjustments_019c8c1c-a77a-7f50-96bc-45fb106ae824" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationTaxContingencies_9f132154-4472-40f5-939d-31078f6b7975" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationTaxContingencies"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract_019b4a21-d573-7e39-94ea-143923f5f161" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationTaxContingencies_9f132154-4472-40f5-939d-31078f6b7975" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationTaxCreditsResearch_fe91b953-69c3-445d-a6e9-89632f25f18d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationTaxCreditsResearch"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract_019b4a21-d573-7e39-94ea-143923f5f161" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationTaxCreditsResearch_fe91b953-69c3-445d-a6e9-89632f25f18d" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_EffectiveIncomeTaxRateReconciliationWithholdingTaxPercent_e6ab30db-50a2-41c6-a3d4-e2f8154cc9d4" xlink:href="ftre-20251231.xsd#ftre_EffectiveIncomeTaxRateReconciliationWithholdingTaxPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract_019b4a21-d573-7e39-94ea-143923f5f161" xlink:to="loc_ftre_EffectiveIncomeTaxRateReconciliationWithholdingTaxPercent_e6ab30db-50a2-41c6-a3d4-e2f8154cc9d4" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateReconciliationBeatPercent_0e58d164-7afa-4911-93ef-81d74eb10b5f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EffectiveIncomeTaxRateReconciliationBeatPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract_019b4a21-d573-7e39-94ea-143923f5f161" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateReconciliationBeatPercent_0e58d164-7afa-4911-93ef-81d74eb10b5f" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_EffectiveIncomeTaxRateReconciliationAdjustmentToPreviouslyCapitalizedExpensesPercent_58bf176d-d4b0-4980-af62-2d67ac97be98" xlink:href="ftre-20251231.xsd#ftre_EffectiveIncomeTaxRateReconciliationAdjustmentToPreviouslyCapitalizedExpensesPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract_019b4a21-d573-7e39-94ea-143923f5f161" xlink:to="loc_ftre_EffectiveIncomeTaxRateReconciliationAdjustmentToPreviouslyCapitalizedExpensesPercent_58bf176d-d4b0-4980-af62-2d67ac97be98" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperations_c453bfc1-ab91-454e-833b-e0f927f864bc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EffectiveIncomeTaxRateContinuingOperations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperationsTaxRateReconciliationAbstract_019b4a21-d573-7e39-94ea-143923f5f161" xlink:to="loc_us-gaap_EffectiveIncomeTaxRateContinuingOperations_c453bfc1-ab91-454e-833b-e0f927f864bc" xlink:type="arc" order="18"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fortrea.com/role/INCOMETAXESNarrativeDetails" xlink:type="simple" xlink:href="ftre-20251231.xsd#INCOMETAXESNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.fortrea.com/role/INCOMETAXESNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLossCarryforwardsLineItems_43e9ba6c-b416-4acd-bb9e-761e53cdc4f1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingLossCarryforwardsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLossCarryforwardsTable_89b4adc1-3f77-4072-85b8-e45f0edf6659" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingLossCarryforwardsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_OperatingLossCarryforwardsLineItems_43e9ba6c-b416-4acd-bb9e-761e53cdc4f1" xlink:to="loc_us-gaap_OperatingLossCarryforwardsTable_89b4adc1-3f77-4072-85b8-e45f0edf6659" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityAxis_d6bafea1-7b1b-431c-b5d4-fbb303e92cd3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxAuthorityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_OperatingLossCarryforwardsTable_89b4adc1-3f77-4072-85b8-e45f0edf6659" xlink:to="loc_us-gaap_IncomeTaxAuthorityAxis_d6bafea1-7b1b-431c-b5d4-fbb303e92cd3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_d6bafea1-7b1b-431c-b5d4-fbb303e92cd3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxAuthorityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_d6bafea1-7b1b-431c-b5d4-fbb303e92cd3" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_d6bafea1-7b1b-431c-b5d4-fbb303e92cd3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxAuthorityDomain_803dcf3a-3c16-498e-9516-bb2036761847" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxAuthorityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeTaxAuthorityAxis_d6bafea1-7b1b-431c-b5d4-fbb303e92cd3" xlink:to="loc_us-gaap_IncomeTaxAuthorityDomain_803dcf3a-3c16-498e-9516-bb2036761847" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DomesticCountryMember_3902f46e-b64f-4dd7-a828-49a57ae7c46a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DomesticCountryMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeTaxAuthorityDomain_803dcf3a-3c16-498e-9516-bb2036761847" xlink:to="loc_us-gaap_DomesticCountryMember_3902f46e-b64f-4dd7-a828-49a57ae7c46a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StateAndLocalJurisdictionMember_e3eee6da-9e1b-47c0-bcb8-e312f6ee862f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StateAndLocalJurisdictionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DomesticCountryMember_3902f46e-b64f-4dd7-a828-49a57ae7c46a" xlink:to="loc_us-gaap_StateAndLocalJurisdictionMember_e3eee6da-9e1b-47c0-bcb8-e312f6ee862f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxCreditCarryforwardAxis_2cd11a41-f108-49bc-bb24-e0301f927af6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TaxCreditCarryforwardAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_OperatingLossCarryforwardsTable_89b4adc1-3f77-4072-85b8-e45f0edf6659" xlink:to="loc_us-gaap_TaxCreditCarryforwardAxis_2cd11a41-f108-49bc-bb24-e0301f927af6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxCreditCarryforwardNameDomain_2cd11a41-f108-49bc-bb24-e0301f927af6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TaxCreditCarryforwardNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TaxCreditCarryforwardAxis_2cd11a41-f108-49bc-bb24-e0301f927af6" xlink:to="loc_us-gaap_TaxCreditCarryforwardNameDomain_2cd11a41-f108-49bc-bb24-e0301f927af6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TaxCreditCarryforwardNameDomain_45b0810d-b2cb-40c4-abf1-f89d02bf84d8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TaxCreditCarryforwardNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TaxCreditCarryforwardAxis_2cd11a41-f108-49bc-bb24-e0301f927af6" xlink:to="loc_us-gaap_TaxCreditCarryforwardNameDomain_45b0810d-b2cb-40c4-abf1-f89d02bf84d8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_InterestExpenseCarryforwardMember_bb9dffae-125b-4257-b7a2-6d6f8da43bca" xlink:href="ftre-20251231.xsd#ftre_InterestExpenseCarryforwardMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TaxCreditCarryforwardNameDomain_45b0810d-b2cb-40c4-abf1-f89d02bf84d8" xlink:to="loc_ftre_InterestExpenseCarryforwardMember_bb9dffae-125b-4257-b7a2-6d6f8da43bca" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxAssetsValuationAllowance_900bbca8-6c52-49f6-b09c-a6c160f8a739" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DeferredTaxAssetsValuationAllowance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLossCarryforwardsLineItems_43e9ba6c-b416-4acd-bb9e-761e53cdc4f1" xlink:to="loc_us-gaap_DeferredTaxAssetsValuationAllowance_900bbca8-6c52-49f6-b09c-a6c160f8a739" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsDomestic_019c35ae-297d-7c69-914b-0bafc1ba5740" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsDomestic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLossCarryforwardsLineItems_43e9ba6c-b416-4acd-bb9e-761e53cdc4f1" xlink:to="loc_us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsDomestic_019c35ae-297d-7c69-914b-0bafc1ba5740" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsStateAndLocal_a4792f6e-b15b-49b7-b283-5d3b10ade11c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsStateAndLocal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLossCarryforwardsLineItems_43e9ba6c-b416-4acd-bb9e-761e53cdc4f1" xlink:to="loc_us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsStateAndLocal_a4792f6e-b15b-49b7-b283-5d3b10ade11c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsSubjectToExpiration_c686faea-acd5-48ff-acb8-9d69c3e23558" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsSubjectToExpiration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLossCarryforwardsLineItems_43e9ba6c-b416-4acd-bb9e-761e53cdc4f1" xlink:to="loc_us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsSubjectToExpiration_c686faea-acd5-48ff-acb8-9d69c3e23558" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsNotSubjectToExpiration_4401105d-d2af-44cd-9852-b16a2bd49173" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsNotSubjectToExpiration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLossCarryforwardsLineItems_43e9ba6c-b416-4acd-bb9e-761e53cdc4f1" xlink:to="loc_us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsNotSubjectToExpiration_4401105d-d2af-44cd-9852-b16a2bd49173" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsForeign_e219b43e-d183-4db5-b522-ac257bf5650d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsForeign"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLossCarryforwardsLineItems_43e9ba6c-b416-4acd-bb9e-761e53cdc4f1" xlink:to="loc_us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsForeign_e219b43e-d183-4db5-b522-ac257bf5650d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SignificantChangeInUnrecognizedTaxBenefitsIsReasonablyPossibleAmountOfUnrecordedBenefit_eb954983-586a-4a5a-9bc7-2960c2562961" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SignificantChangeInUnrecognizedTaxBenefitsIsReasonablyPossibleAmountOfUnrecordedBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLossCarryforwardsLineItems_43e9ba6c-b416-4acd-bb9e-761e53cdc4f1" xlink:to="loc_us-gaap_SignificantChangeInUnrecognizedTaxBenefitsIsReasonablyPossibleAmountOfUnrecordedBenefit_eb954983-586a-4a5a-9bc7-2960c2562961" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestExpense_a77799d0-a9e0-48b8-a63b-9b9f7f155d6f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLossCarryforwardsLineItems_43e9ba6c-b416-4acd-bb9e-761e53cdc4f1" xlink:to="loc_us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestExpense_a77799d0-a9e0-48b8-a63b-9b9f7f155d6f" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate_259dce5a-a1ed-48b3-99c5-70b43474ad67" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLossCarryforwardsLineItems_43e9ba6c-b416-4acd-bb9e-761e53cdc4f1" xlink:to="loc_us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate_259dce5a-a1ed-48b3-99c5-70b43474ad67" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredTaxLiabilitiesUndistributedForeignEarnings_26a95074-8f4f-42a8-a7fa-dd2133281d05" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DeferredTaxLiabilitiesUndistributedForeignEarnings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingLossCarryforwardsLineItems_43e9ba6c-b416-4acd-bb9e-761e53cdc4f1" xlink:to="loc_us-gaap_DeferredTaxLiabilitiesUndistributedForeignEarnings_26a95074-8f4f-42a8-a7fa-dd2133281d05" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fortrea.com/role/STOCKCOMPENSATIONPLANSNarrativeDetails" xlink:type="simple" xlink:href="ftre-20251231.xsd#STOCKCOMPENSATIONPLANSNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.fortrea.com/role/STOCKCOMPENSATIONPLANSNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_76377b40-7cc8-4188-aace-7f4ac6c4585d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_34a1b8f5-4aa5-4039-b6fa-6318bc900ea2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_76377b40-7cc8-4188-aace-7f4ac6c4585d" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_34a1b8f5-4aa5-4039-b6fa-6318bc900ea2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_d8f7a385-6a57-4915-a785-3ef6978b07e1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_34a1b8f5-4aa5-4039-b6fa-6318bc900ea2" xlink:to="loc_us-gaap_AwardTypeAxis_d8f7a385-6a57-4915-a785-3ef6978b07e1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_d8f7a385-6a57-4915-a785-3ef6978b07e1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_d8f7a385-6a57-4915-a785-3ef6978b07e1" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_d8f7a385-6a57-4915-a785-3ef6978b07e1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_aa9cf9a2-e36e-480a-8ea3-ad75ab28b1dd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_d8f7a385-6a57-4915-a785-3ef6978b07e1" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_aa9cf9a2-e36e-480a-8ea3-ad75ab28b1dd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_RestrictedStockRestrictedStockUnitsAndPerformanceSharesMember_7b6b8c97-7edc-4331-82f7-f76769250d74" xlink:href="ftre-20251231.xsd#ftre_RestrictedStockRestrictedStockUnitsAndPerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_aa9cf9a2-e36e-480a-8ea3-ad75ab28b1dd" xlink:to="loc_ftre_RestrictedStockRestrictedStockUnitsAndPerformanceSharesMember_7b6b8c97-7edc-4331-82f7-f76769250d74" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_a4111cc5-d486-4d21-82c8-11999c05adea" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ftre_RestrictedStockRestrictedStockUnitsAndPerformanceSharesMember_7b6b8c97-7edc-4331-82f7-f76769250d74" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_a4111cc5-d486-4d21-82c8-11999c05adea" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_f03d7864-0d12-4d51-b6bc-6d753fb3f761" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ftre_RestrictedStockRestrictedStockUnitsAndPerformanceSharesMember_7b6b8c97-7edc-4331-82f7-f76769250d74" xlink:to="loc_us-gaap_PerformanceSharesMember_f03d7864-0d12-4d51-b6bc-6d753fb3f761" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_e9c93bcc-0ca3-4bce-8634-332bd880c56b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_aa9cf9a2-e36e-480a-8ea3-ad75ab28b1dd" xlink:to="loc_us-gaap_EmployeeStockOptionMember_e9c93bcc-0ca3-4bce-8634-332bd880c56b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_99f4a02f-e73d-4ed2-852d-d31ebec1e6a3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_34a1b8f5-4aa5-4039-b6fa-6318bc900ea2" xlink:to="loc_us-gaap_PlanNameAxis_99f4a02f-e73d-4ed2-852d-d31ebec1e6a3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_99f4a02f-e73d-4ed2-852d-d31ebec1e6a3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_99f4a02f-e73d-4ed2-852d-d31ebec1e6a3" xlink:to="loc_us-gaap_PlanNameDomain_99f4a02f-e73d-4ed2-852d-d31ebec1e6a3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_92faebcd-e3fe-4abc-8226-1d6f3969f8db" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_99f4a02f-e73d-4ed2-852d-d31ebec1e6a3" xlink:to="loc_us-gaap_PlanNameDomain_92faebcd-e3fe-4abc-8226-1d6f3969f8db" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_FortreasOmnibusIncentivePlanMember_841a996f-c59e-4977-91e6-c292642e26c9" xlink:href="ftre-20251231.xsd#ftre_FortreasOmnibusIncentivePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_92faebcd-e3fe-4abc-8226-1d6f3969f8db" xlink:to="loc_ftre_FortreasOmnibusIncentivePlanMember_841a996f-c59e-4977-91e6-c292642e26c9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_FortreasEmployeeStockPurchasePlanMember_71354c72-0a0b-44a5-a9b7-0ed4e0bd53c4" xlink:href="ftre-20251231.xsd#ftre_FortreasEmployeeStockPurchasePlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_92faebcd-e3fe-4abc-8226-1d6f3969f8db" xlink:to="loc_ftre_FortreasEmployeeStockPurchasePlanMember_71354c72-0a0b-44a5-a9b7-0ed4e0bd53c4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_InducementPlanMember_019c1bf2-b83f-7b5d-91eb-c57d125d1f69" xlink:href="ftre-20251231.xsd#ftre_InducementPlanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_92faebcd-e3fe-4abc-8226-1d6f3969f8db" xlink:to="loc_ftre_InducementPlanMember_019c1bf2-b83f-7b5d-91eb-c57d125d1f69" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GranteeStatusAxis_b123e135-93a7-4a7b-8d48-14f842ec1a14" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GranteeStatusAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_34a1b8f5-4aa5-4039-b6fa-6318bc900ea2" xlink:to="loc_us-gaap_GranteeStatusAxis_b123e135-93a7-4a7b-8d48-14f842ec1a14" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GranteeStatusDomain_b123e135-93a7-4a7b-8d48-14f842ec1a14_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GranteeStatusDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_GranteeStatusAxis_b123e135-93a7-4a7b-8d48-14f842ec1a14" xlink:to="loc_us-gaap_GranteeStatusDomain_b123e135-93a7-4a7b-8d48-14f842ec1a14_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GranteeStatusDomain_598c7f7e-0376-4244-ae7e-def41d357c49" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GranteeStatusDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_GranteeStatusAxis_b123e135-93a7-4a7b-8d48-14f842ec1a14" xlink:to="loc_us-gaap_GranteeStatusDomain_598c7f7e-0376-4244-ae7e-def41d357c49" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedPaymentArrangementEmployeeMember_e6b6a5d5-fb3d-4717-bb5d-c74cdb12e9dc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedPaymentArrangementEmployeeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GranteeStatusDomain_598c7f7e-0376-4244-ae7e-def41d357c49" xlink:to="loc_us-gaap_ShareBasedPaymentArrangementEmployeeMember_e6b6a5d5-fb3d-4717-bb5d-c74cdb12e9dc" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedPaymentArrangementNonemployeeMember_cf11c357-28b3-4c90-b85b-25bcd381fc34" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedPaymentArrangementNonemployeeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GranteeStatusDomain_598c7f7e-0376-4244-ae7e-def41d357c49" xlink:to="loc_us-gaap_ShareBasedPaymentArrangementNonemployeeMember_cf11c357-28b3-4c90-b85b-25bcd381fc34" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingAxis_4f842cf7-68ac-4087-917c-facdf0143bda" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VestingAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_34a1b8f5-4aa5-4039-b6fa-6318bc900ea2" xlink:to="loc_us-gaap_VestingAxis_4f842cf7-68ac-4087-917c-facdf0143bda" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingDomain_4f842cf7-68ac-4087-917c-facdf0143bda_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VestingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VestingAxis_4f842cf7-68ac-4087-917c-facdf0143bda" xlink:to="loc_us-gaap_VestingDomain_4f842cf7-68ac-4087-917c-facdf0143bda_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingDomain_ceab06c4-f343-4db5-8abb-500b58049c1f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VestingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VestingAxis_4f842cf7-68ac-4087-917c-facdf0143bda" xlink:to="loc_us-gaap_VestingDomain_ceab06c4-f343-4db5-8abb-500b58049c1f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheOneMember_8cfabee6-a718-4b64-b025-1977571dd36a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationAwardTrancheOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_ceab06c4-f343-4db5-8abb-500b58049c1f" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheOneMember_8cfabee6-a718-4b64-b025-1977571dd36a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheTwoMember_b99e907f-e90b-4dc7-aec1-918e7ab6851f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationAwardTrancheTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_ceab06c4-f343-4db5-8abb-500b58049c1f" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheTwoMember_b99e907f-e90b-4dc7-aec1-918e7ab6851f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheThreeMember_410995f6-901c-4146-97c0-943b1fc82630" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationAwardTrancheThreeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_ceab06c4-f343-4db5-8abb-500b58049c1f" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheThreeMember_410995f6-901c-4146-97c0-943b1fc82630" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedUponConversion_6812a033-bad5-4f94-b5e2-fe94980f52c3" xlink:href="ftre-20251231.xsd#ftre_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedUponConversion"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_76377b40-7cc8-4188-aace-7f4ac6c4585d" xlink:to="loc_ftre_ShareBasedCompensationArrangementByShareBasedPaymentAwardSharesIssuedUponConversion_6812a033-bad5-4f94-b5e2-fe94980f52c3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_c99a8880-5f6f-4142-b415-81698fc95cb5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_76377b40-7cc8-4188-aace-7f4ac6c4585d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_c99a8880-5f6f-4142-b415-81698fc95cb5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_2ef09754-2df5-4764-aafc-86487d9bc3db" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_76377b40-7cc8-4188-aace-7f4ac6c4585d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_2ef09754-2df5-4764-aafc-86487d9bc3db" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_3d42b03d-02a7-4767-830c-ca94465bdb6a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_76377b40-7cc8-4188-aace-7f4ac6c4585d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_3d42b03d-02a7-4767-830c-ca94465bdb6a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_457c8739-517d-42d4-a6e9-27a5ca33b432" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_76377b40-7cc8-4188-aace-7f4ac6c4585d" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardExpirationPeriod_457c8739-517d-42d4-a6e9-27a5ca33b432" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_c505a44c-c7f0-4004-8c3f-662447aebfbf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_76377b40-7cc8-4188-aace-7f4ac6c4585d" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_c505a44c-c7f0-4004-8c3f-662447aebfbf" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_ShareBasedCompensationArrangementByShareBasedPaymentAwardCliffVestingPeriod_0451ee29-c9c1-4adc-86a1-deb312c8b47a" xlink:href="ftre-20251231.xsd#ftre_ShareBasedCompensationArrangementByShareBasedPaymentAwardCliffVestingPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_76377b40-7cc8-4188-aace-7f4ac6c4585d" xlink:to="loc_ftre_ShareBasedCompensationArrangementByShareBasedPaymentAwardCliffVestingPeriod_0451ee29-c9c1-4adc-86a1-deb312c8b47a" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_7567ed21-675f-459e-abd2-473306486952" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_76377b40-7cc8-4188-aace-7f4ac6c4585d" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized_7567ed21-675f-459e-abd2-473306486952" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_3a1c4499-ac42-495c-bbcc-f740ddea0fb0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_76377b40-7cc8-4188-aace-7f4ac6c4585d" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_3a1c4499-ac42-495c-bbcc-f740ddea0fb0" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_4e600e2d-15b1-44cf-a9aa-d9ebb9f35dd6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_76377b40-7cc8-4188-aace-7f4ac6c4585d" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_4e600e2d-15b1-44cf-a9aa-d9ebb9f35dd6" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage_a3b38c84-eeff-47c9-9d61-c0e738492246" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_76377b40-7cc8-4188-aace-7f4ac6c4585d" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage_a3b38c84-eeff-47c9-9d61-c0e738492246" xlink:type="arc" order="10"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fortrea.com/role/STOCKCOMPENSATIONPLANSRestrictedStockUnitsandPerformanceSharesDetails" xlink:type="simple" xlink:href="ftre-20251231.xsd#STOCKCOMPENSATIONPLANSRestrictedStockUnitsandPerformanceSharesDetails"/>
  <link:definitionLink xlink:role="http://www.fortrea.com/role/STOCKCOMPENSATIONPLANSRestrictedStockUnitsandPerformanceSharesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_1e2210c2-175a-4eae-af87-858a3f61484e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_762e2ed6-9e23-429a-811d-8cecee13bcc8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_1e2210c2-175a-4eae-af87-858a3f61484e" xlink:to="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_762e2ed6-9e23-429a-811d-8cecee13bcc8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_d3021498-bdb8-43a6-9e22-e0880ada4903" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_762e2ed6-9e23-429a-811d-8cecee13bcc8" xlink:to="loc_us-gaap_AwardTypeAxis_d3021498-bdb8-43a6-9e22-e0880ada4903" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_d3021498-bdb8-43a6-9e22-e0880ada4903_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_d3021498-bdb8-43a6-9e22-e0880ada4903" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_d3021498-bdb8-43a6-9e22-e0880ada4903_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_046b1c66-6ee6-4aec-bd6f-ff0f43cb66c1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_d3021498-bdb8-43a6-9e22-e0880ada4903" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_046b1c66-6ee6-4aec-bd6f-ff0f43cb66c1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_83c51947-91c2-4281-b8e2-0ecb39be36bb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_046b1c66-6ee6-4aec-bd6f-ff0f43cb66c1" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_83c51947-91c2-4281-b8e2-0ecb39be36bb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_a6f64634-8a77-469d-a787-a642bc0cc45d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_046b1c66-6ee6-4aec-bd6f-ff0f43cb66c1" xlink:to="loc_us-gaap_PerformanceSharesMember_a6f64634-8a77-469d-a787-a642bc0cc45d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_a3893e7c-1410-497b-a69d-c2e6fec3d5c6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_1e2210c2-175a-4eae-af87-858a3f61484e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_a3893e7c-1410-497b-a69d-c2e6fec3d5c6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_52f9ddc4-3a28-4df1-9c0f-20e3811a4597" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_a3893e7c-1410-497b-a69d-c2e6fec3d5c6" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_52f9ddc4-3a28-4df1-9c0f-20e3811a4597" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_ed32c46d-35c0-48ca-af3e-ca807324b365" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_a3893e7c-1410-497b-a69d-c2e6fec3d5c6" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_ed32c46d-35c0-48ca-af3e-ca807324b365" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_967642df-b2d4-4412-a0df-b20d4fc2f342" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_a3893e7c-1410-497b-a69d-c2e6fec3d5c6" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_967642df-b2d4-4412-a0df-b20d4fc2f342" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_7962c9dc-5d9b-4ffd-b7ee-678bceee4f58" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_a3893e7c-1410-497b-a69d-c2e6fec3d5c6" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_7962c9dc-5d9b-4ffd-b7ee-678bceee4f58" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_e0ddf932-9f95-418d-b2ca-355be8b4bb8c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_24a6d6b6-fe1a-41ed-9d7a-694f84b02d13" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_1e2210c2-175a-4eae-af87-858a3f61484e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_24a6d6b6-fe1a-41ed-9d7a-694f84b02d13" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_ed1be76d-b21c-4519-8cd9-471cf48321c7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_24a6d6b6-fe1a-41ed-9d7a-694f84b02d13" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_ed1be76d-b21c-4519-8cd9-471cf48321c7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_ccacd691-f3c6-46c9-8f1e-d24acfa6e26e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_24a6d6b6-fe1a-41ed-9d7a-694f84b02d13" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_ccacd691-f3c6-46c9-8f1e-d24acfa6e26e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_6c487ef7-d6f1-41b0-a82f-927bfee9cceb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_24a6d6b6-fe1a-41ed-9d7a-694f84b02d13" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_6c487ef7-d6f1-41b0-a82f-927bfee9cceb" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_a3c37136-611c-46a0-b1a2-37260bbccdca" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_24a6d6b6-fe1a-41ed-9d7a-694f84b02d13" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_a3c37136-611c-46a0-b1a2-37260bbccdca" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_0aa4b1b5-5a76-4d3a-89af-3246ca798770" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fortrea.com/role/STOCKCOMPENSATIONPLANSShareBasedCompensationExpenseDetails" xlink:type="simple" xlink:href="ftre-20251231.xsd#STOCKCOMPENSATIONPLANSShareBasedCompensationExpenseDetails"/>
  <link:definitionLink xlink:role="http://www.fortrea.com/role/STOCKCOMPENSATIONPLANSShareBasedCompensationExpenseDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_63e947bd-c074-4ab4-af3f-c38d2ffd0c86" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_86abd5fd-8337-4239-841f-7a50b2073cf4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_63e947bd-c074-4ab4-af3f-c38d2ffd0c86" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_86abd5fd-8337-4239-841f-7a50b2073cf4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_438e3cc6-2e2d-4cae-b00e-20e09d4329c8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_86abd5fd-8337-4239-841f-7a50b2073cf4" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_438e3cc6-2e2d-4cae-b00e-20e09d4329c8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_438e3cc6-2e2d-4cae-b00e-20e09d4329c8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_438e3cc6-2e2d-4cae-b00e-20e09d4329c8" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_438e3cc6-2e2d-4cae-b00e-20e09d4329c8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_1b3bcf04-5430-43cb-b798-d38868f6d513" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_438e3cc6-2e2d-4cae-b00e-20e09d4329c8" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_1b3bcf04-5430-43cb-b798-d38868f6d513" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfSalesMember_d02388b9-6b7c-4f00-8dac-7f5897293219" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CostOfSalesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_1b3bcf04-5430-43cb-b798-d38868f6d513" xlink:to="loc_us-gaap_CostOfSalesMember_d02388b9-6b7c-4f00-8dac-7f5897293219" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingGeneralAndAdministrativeExpensesMember_8fd48a58-d0b8-4d1f-94ba-c5da6d34b31c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SellingGeneralAndAdministrativeExpensesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_1b3bcf04-5430-43cb-b798-d38868f6d513" xlink:to="loc_us-gaap_SellingGeneralAndAdministrativeExpensesMember_8fd48a58-d0b8-4d1f-94ba-c5da6d34b31c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_75797fdc-0d0e-4487-82f6-c821690e1197" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_63e947bd-c074-4ab4-af3f-c38d2ffd0c86" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_75797fdc-0d0e-4487-82f6-c821690e1197" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense_724c4ba9-8c6e-4ea5-87b2-288c3843c89c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_63e947bd-c074-4ab4-af3f-c38d2ffd0c86" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense_724c4ba9-8c6e-4ea5-87b2-288c3843c89c" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fortrea.com/role/PREFERREDSTOCKANDCOMMONSHAREHOLDERSEQUITYNarrativeDetails" xlink:type="simple" xlink:href="ftre-20251231.xsd#PREFERREDSTOCKANDCOMMONSHAREHOLDERSEQUITYNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.fortrea.com/role/PREFERREDSTOCKANDCOMMONSHAREHOLDERSEQUITYNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_7dccd10a-3a1e-48d2-b4e9-c66a4941c9b7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_5e144dc1-9566-42e9-bced-394e7a11f6af" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_7dccd10a-3a1e-48d2-b4e9-c66a4941c9b7" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_5e144dc1-9566-42e9-bced-394e7a11f6af" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightAxis_4f61dc3a-860a-4bf5-85dd-0b68da012e7b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_5e144dc1-9566-42e9-bced-394e7a11f6af" xlink:to="loc_us-gaap_ClassOfWarrantOrRightAxis_4f61dc3a-860a-4bf5-85dd-0b68da012e7b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_4f61dc3a-860a-4bf5-85dd-0b68da012e7b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_4f61dc3a-860a-4bf5-85dd-0b68da012e7b" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_4f61dc3a-860a-4bf5-85dd-0b68da012e7b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightDomain_48cee53b-099f-4f49-a335-ac76f5ff1077" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ClassOfWarrantOrRightAxis_4f61dc3a-860a-4bf5-85dd-0b68da012e7b" xlink:to="loc_us-gaap_ClassOfWarrantOrRightDomain_48cee53b-099f-4f49-a335-ac76f5ff1077" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RightsMember_4fb8eddd-8c9c-43d0-8425-cd06098112ab" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RightsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfWarrantOrRightDomain_48cee53b-099f-4f49-a335-ac76f5ff1077" xlink:to="loc_us-gaap_RightsMember_4fb8eddd-8c9c-43d0-8425-cd06098112ab" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019b0b41-2002-7a9f-807f-c6f22fb026fb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_5e144dc1-9566-42e9-bced-394e7a11f6af" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019b0b41-2002-7a9f-807f-c6f22fb026fb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019b0b41-2002-7a9f-807f-c6f22fb026fb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019b0b41-2002-7a9f-807f-c6f22fb026fb" xlink:to="loc_us-gaap_ClassOfStockDomain_019b0b41-2002-7a9f-807f-c6f22fb026fb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019b0b41-2002-784a-bb97-955f644ad8da" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019b0b41-2002-7a9f-807f-c6f22fb026fb" xlink:to="loc_us-gaap_ClassOfStockDomain_019b0b41-2002-784a-bb97-955f644ad8da" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeriesAPreferredStockMember_019b0b41-2002-7798-a713-e028907993d9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SeriesAPreferredStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019b0b41-2002-784a-bb97-955f644ad8da" xlink:to="loc_us-gaap_SeriesAPreferredStockMember_019b0b41-2002-7798-a713-e028907993d9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_CommonStockSharesIssuedNotDisclosed_019c8c13-9fb6-7227-8761-fd8ac7331a2f" xlink:href="ftre-20251231.xsd#ftre_CommonStockSharesIssuedNotDisclosed"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_7dccd10a-3a1e-48d2-b4e9-c66a4941c9b7" xlink:to="loc_ftre_CommonStockSharesIssuedNotDisclosed_019c8c13-9fb6-7227-8761-fd8ac7331a2f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_6a236e95-244c-4da7-9857-95383f6f1bf0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_7dccd10a-3a1e-48d2-b4e9-c66a4941c9b7" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_6a236e95-244c-4da7-9857-95383f6f1bf0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_1e2c715f-6bfa-4b88-8b6c-52ada84c95f0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_7dccd10a-3a1e-48d2-b4e9-c66a4941c9b7" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_1e2c715f-6bfa-4b88-8b6c-52ada84c95f0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesAuthorized_403c4f5e-dc57-4720-a81e-f4b8907925e6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PreferredStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_7dccd10a-3a1e-48d2-b4e9-c66a4941c9b7" xlink:to="loc_us-gaap_PreferredStockSharesAuthorized_403c4f5e-dc57-4720-a81e-f4b8907925e6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockParOrStatedValuePerShare_73743fee-edde-417b-9386-e5c1f534571b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PreferredStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_7dccd10a-3a1e-48d2-b4e9-c66a4941c9b7" xlink:to="loc_us-gaap_PreferredStockParOrStatedValuePerShare_73743fee-edde-417b-9386-e5c1f534571b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesOutstanding_56bda0f5-0d50-4924-947c-26303e2cd51b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PreferredStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_7dccd10a-3a1e-48d2-b4e9-c66a4941c9b7" xlink:to="loc_us-gaap_PreferredStockSharesOutstanding_56bda0f5-0d50-4924-947c-26303e2cd51b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_ClassOfWarrantOrRightNumberOfRightsPerCommonStockShare_d52c7f66-daf3-4d87-80f6-ebbd08f4f540" xlink:href="ftre-20251231.xsd#ftre_ClassOfWarrantOrRightNumberOfRightsPerCommonStockShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_7dccd10a-3a1e-48d2-b4e9-c66a4941c9b7" xlink:to="loc_ftre_ClassOfWarrantOrRightNumberOfRightsPerCommonStockShare_d52c7f66-daf3-4d87-80f6-ebbd08f4f540" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByEachWarrantOrRight_019b0b41-2002-7912-ae4c-2af16a7d6aff" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByEachWarrantOrRight"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_7dccd10a-3a1e-48d2-b4e9-c66a4941c9b7" xlink:to="loc_us-gaap_ClassOfWarrantOrRightNumberOfSecuritiesCalledByEachWarrantOrRight_019b0b41-2002-7912-ae4c-2af16a7d6aff" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_6eabc372-f3dc-4c47-aff8-3a507f66ca00" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_7dccd10a-3a1e-48d2-b4e9-c66a4941c9b7" xlink:to="loc_us-gaap_ClassOfWarrantOrRightExercisePriceOfWarrantsOrRights1_6eabc372-f3dc-4c47-aff8-3a507f66ca00" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_ClassOfWarrantOrRightBeneficialOwnershipAcquiredPercentage_f4693011-8c7e-4803-b381-1dea1f02333d" xlink:href="ftre-20251231.xsd#ftre_ClassOfWarrantOrRightBeneficialOwnershipAcquiredPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_7dccd10a-3a1e-48d2-b4e9-c66a4941c9b7" xlink:to="loc_ftre_ClassOfWarrantOrRightBeneficialOwnershipAcquiredPercentage_f4693011-8c7e-4803-b381-1dea1f02333d" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_ClassOfWarrantOrRightSecurityCalledByEachWarrantOrRightValueMultiple_ede89137-4ea1-4e1f-8da9-71bdb6be544a" xlink:href="ftre-20251231.xsd#ftre_ClassOfWarrantOrRightSecurityCalledByEachWarrantOrRightValueMultiple"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_7dccd10a-3a1e-48d2-b4e9-c66a4941c9b7" xlink:to="loc_ftre_ClassOfWarrantOrRightSecurityCalledByEachWarrantOrRightValueMultiple_ede89137-4ea1-4e1f-8da9-71bdb6be544a" xlink:type="arc" order="10"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fortrea.com/role/PREFERREDSTOCKANDCOMMONSHAREHOLDERSEQUITYScheduleofAccumulatedOtherComprehensiveLossDetails" xlink:type="simple" xlink:href="ftre-20251231.xsd#PREFERREDSTOCKANDCOMMONSHAREHOLDERSEQUITYScheduleofAccumulatedOtherComprehensiveLossDetails"/>
  <link:definitionLink xlink:role="http://www.fortrea.com/role/PREFERREDSTOCKANDCOMMONSHAREHOLDERSEQUITYScheduleofAccumulatedOtherComprehensiveLossDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_b6fef588-2cc2-4646-9745-17a4d88f3651" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_889cf284-64ac-4566-9863-6fc6278e95a4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_b6fef588-2cc2-4646-9745-17a4d88f3651" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_889cf284-64ac-4566-9863-6fc6278e95a4" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_27fa85f7-85d4-44bc-a66b-d32b93b7034d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_889cf284-64ac-4566-9863-6fc6278e95a4" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_27fa85f7-85d4-44bc-a66b-d32b93b7034d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_27fa85f7-85d4-44bc-a66b-d32b93b7034d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_27fa85f7-85d4-44bc-a66b-d32b93b7034d" xlink:to="loc_us-gaap_EquityComponentDomain_27fa85f7-85d4-44bc-a66b-d32b93b7034d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_29434b96-f237-4bcb-afe7-930161d57728" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_27fa85f7-85d4-44bc-a66b-d32b93b7034d" xlink:to="loc_us-gaap_EquityComponentDomain_29434b96-f237-4bcb-afe7-930161d57728" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_90a9e46a-6f99-4c67-a26c-fd4d1c3d50ca" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_29434b96-f237-4bcb-afe7-930161d57728" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_90a9e46a-6f99-4c67-a26c-fd4d1c3d50ca" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedTranslationAdjustmentMember_80810f54-069c-46cd-8ad4-324c03774e2a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedTranslationAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_90a9e46a-6f99-4c67-a26c-fd4d1c3d50ca" xlink:to="loc_us-gaap_AccumulatedTranslationAdjustmentMember_80810f54-069c-46cd-8ad4-324c03774e2a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_0e1c30c4-8573-4ed3-9126-ba1c5c843dda" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_90a9e46a-6f99-4c67-a26c-fd4d1c3d50ca" xlink:to="loc_us-gaap_AccumulatedDefinedBenefitPlansAdjustmentMember_0e1c30c4-8573-4ed3-9126-ba1c5c843dda" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember_6a517176-e71e-4183-bf2f-a2a638aba891" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_90a9e46a-6f99-4c67-a26c-fd4d1c3d50ca" xlink:to="loc_us-gaap_AccumulatedGainLossNetCashFlowHedgeParentMember_6a517176-e71e-4183-bf2f-a2a638aba891" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_c5e68757-6b5e-4f96-b563-2cb178cfc923" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AOCIAttributableToParentNetOfTaxRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_b6fef588-2cc2-4646-9745-17a4d88f3651" xlink:to="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_c5e68757-6b5e-4f96-b563-2cb178cfc923" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_9481737f-7bde-4ad3-ae39-bac34838f9df" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_c5e68757-6b5e-4f96-b563-2cb178cfc923" xlink:to="loc_us-gaap_StockholdersEquity_9481737f-7bde-4ad3-ae39-bac34838f9df" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OciBeforeReclassificationsBeforeTaxAttributableToParent_7b1508a6-d81f-46b1-bd55-66f55a6a0660" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OciBeforeReclassificationsBeforeTaxAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_c5e68757-6b5e-4f96-b563-2cb178cfc923" xlink:to="loc_us-gaap_OciBeforeReclassificationsBeforeTaxAttributableToParent_7b1508a6-d81f-46b1-bd55-66f55a6a0660" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReclassificationFromAociCurrentPeriodBeforeTaxAttributableToParent_6fef0771-50c6-46dc-90ae-4b31614805c2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReclassificationFromAociCurrentPeriodBeforeTaxAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_c5e68757-6b5e-4f96-b563-2cb178cfc923" xlink:to="loc_us-gaap_ReclassificationFromAociCurrentPeriodBeforeTaxAttributableToParent_6fef0771-50c6-46dc-90ae-4b31614805c2" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTranslationAdjustmentTax_63751a0a-21d9-4076-8d61-3e590314e256" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTranslationAdjustmentTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_c5e68757-6b5e-4f96-b563-2cb178cfc923" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTranslationAdjustmentTax_63751a0a-21d9-4076-8d61-3e590314e256" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_f18b2a4a-43c8-4925-81cd-753cf27470e1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquity"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fortrea.com/role/PENSIONANDPOSTRETIREMENTPLANSNarrativeDetails" xlink:type="simple" xlink:href="ftre-20251231.xsd#PENSIONANDPOSTRETIREMENTPLANSNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.fortrea.com/role/PENSIONANDPOSTRETIREMENTPLANSNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedContributionPlanDisclosureLineItems_019c1be4-a6f0-7353-87fd-77c8a5c5df58" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedContributionPlanDisclosureLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedContributionPlanTable_019c1be4-a6f0-7327-8066-5e8422e511bd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedContributionPlanTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DefinedContributionPlanDisclosureLineItems_019c1be4-a6f0-7353-87fd-77c8a5c5df58" xlink:to="loc_us-gaap_DefinedContributionPlanTable_019c1be4-a6f0-7327-8066-5e8422e511bd" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_DefinedContributionPlanVariableComponentAxis_019c1be4-a6f0-772f-9504-42c79739c7ab" xlink:href="ftre-20251231.xsd#ftre_DefinedContributionPlanVariableComponentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DefinedContributionPlanTable_019c1be4-a6f0-7327-8066-5e8422e511bd" xlink:to="loc_ftre_DefinedContributionPlanVariableComponentAxis_019c1be4-a6f0-772f-9504-42c79739c7ab" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_DefinedContributionPlanVariableComponentDomain_019c1be4-a6f0-772f-9504-42c79739c7ab_default" xlink:href="ftre-20251231.xsd#ftre_DefinedContributionPlanVariableComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_ftre_DefinedContributionPlanVariableComponentAxis_019c1be4-a6f0-772f-9504-42c79739c7ab" xlink:to="loc_ftre_DefinedContributionPlanVariableComponentDomain_019c1be4-a6f0-772f-9504-42c79739c7ab_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_DefinedContributionPlanVariableComponentDomain_019c1be4-a6f0-7f82-b7f8-b8109ada07ac" xlink:href="ftre-20251231.xsd#ftre_DefinedContributionPlanVariableComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_ftre_DefinedContributionPlanVariableComponentAxis_019c1be4-a6f0-772f-9504-42c79739c7ab" xlink:to="loc_ftre_DefinedContributionPlanVariableComponentDomain_019c1be4-a6f0-7f82-b7f8-b8109ada07ac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_DefinedContributionPlanVariableComponentOneMember_019c1be4-a6f0-7534-9919-22a3722144a0" xlink:href="ftre-20251231.xsd#ftre_DefinedContributionPlanVariableComponentOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ftre_DefinedContributionPlanVariableComponentDomain_019c1be4-a6f0-7f82-b7f8-b8109ada07ac" xlink:to="loc_ftre_DefinedContributionPlanVariableComponentOneMember_019c1be4-a6f0-7534-9919-22a3722144a0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_DefinedContributionPlanVariableComponentTwoMember_019c1be4-a6f0-794a-93d1-299a38f5466d" xlink:href="ftre-20251231.xsd#ftre_DefinedContributionPlanVariableComponentTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ftre_DefinedContributionPlanVariableComponentDomain_019c1be4-a6f0-7f82-b7f8-b8109ada07ac" xlink:to="loc_ftre_DefinedContributionPlanVariableComponentTwoMember_019c1be4-a6f0-794a-93d1-299a38f5466d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_DefinedContributionPlanAutomaticEnrollmentPercent_019c1be4-a6f0-7906-8f76-42ddc1576ef2" xlink:href="ftre-20251231.xsd#ftre_DefinedContributionPlanAutomaticEnrollmentPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedContributionPlanDisclosureLineItems_019c1be4-a6f0-7353-87fd-77c8a5c5df58" xlink:to="loc_ftre_DefinedContributionPlanAutomaticEnrollmentPercent_019c1be4-a6f0-7906-8f76-42ddc1576ef2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedContributionPlanEmployerMatchingContributionPercentOfMatch_a1f8f490-a46c-4cb6-a174-77ea86e3b7a3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedContributionPlanEmployerMatchingContributionPercentOfMatch"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedContributionPlanDisclosureLineItems_019c1be4-a6f0-7353-87fd-77c8a5c5df58" xlink:to="loc_us-gaap_DefinedContributionPlanEmployerMatchingContributionPercentOfMatch_a1f8f490-a46c-4cb6-a174-77ea86e3b7a3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent_019c0849-100e-7dec-90b3-f54692102319" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedContributionPlanDisclosureLineItems_019c1be4-a6f0-7353-87fd-77c8a5c5df58" xlink:to="loc_us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent_019c0849-100e-7dec-90b3-f54692102319" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedContributionPlanMaximumAnnualContributionsPerEmployeePercent_c2e375c0-79eb-4635-a6ff-b22f903aa1d6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedContributionPlanMaximumAnnualContributionsPerEmployeePercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedContributionPlanDisclosureLineItems_019c1be4-a6f0-7353-87fd-77c8a5c5df58" xlink:to="loc_us-gaap_DefinedContributionPlanMaximumAnnualContributionsPerEmployeePercent_c2e375c0-79eb-4635-a6ff-b22f903aa1d6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedContributionPlanCostRecognized_874ede8f-2b22-4ff2-98ba-e95132135dce" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedContributionPlanCostRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedContributionPlanDisclosureLineItems_019c1be4-a6f0-7353-87fd-77c8a5c5df58" xlink:to="loc_us-gaap_DefinedContributionPlanCostRecognized_874ede8f-2b22-4ff2-98ba-e95132135dce" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanEffectOfOnePercentagePointIncreaseOnServiceAndInterestCostComponents_ad23233e-3e9b-41c3-afdf-5211ec9e6b54" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanEffectOfOnePercentagePointIncreaseOnServiceAndInterestCostComponents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedContributionPlanDisclosureLineItems_019c1be4-a6f0-7353-87fd-77c8a5c5df58" xlink:to="loc_us-gaap_DefinedBenefitPlanEffectOfOnePercentagePointIncreaseOnServiceAndInterestCostComponents_ad23233e-3e9b-41c3-afdf-5211ec9e6b54" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanEffectOfOnePercentagePointDecreaseOnServiceAndInterestCostComponents1_716334a8-166e-45ec-8da5-5b9d0bf6d841" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanEffectOfOnePercentagePointDecreaseOnServiceAndInterestCostComponents1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedContributionPlanDisclosureLineItems_019c1be4-a6f0-7353-87fd-77c8a5c5df58" xlink:to="loc_us-gaap_DefinedBenefitPlanEffectOfOnePercentagePointDecreaseOnServiceAndInterestCostComponents1_716334a8-166e-45ec-8da5-5b9d0bf6d841" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_DefinedBenefitPlanEffectOfOnePercentagePointIncreaseInExpectedReturnOnPlanAssets_2b07e84a-cd2c-489f-9b1a-97fff29b0d59" xlink:href="ftre-20251231.xsd#ftre_DefinedBenefitPlanEffectOfOnePercentagePointIncreaseInExpectedReturnOnPlanAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedContributionPlanDisclosureLineItems_019c1be4-a6f0-7353-87fd-77c8a5c5df58" xlink:to="loc_ftre_DefinedBenefitPlanEffectOfOnePercentagePointIncreaseInExpectedReturnOnPlanAssets_2b07e84a-cd2c-489f-9b1a-97fff29b0d59" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_DefinedBenefitPlanEffectOfOnePercentagePointDecreaseInExpectedReturnOnPlanAssets_aac0cf1e-f9c5-4791-a878-2597e6daadd3" xlink:href="ftre-20251231.xsd#ftre_DefinedBenefitPlanEffectOfOnePercentagePointDecreaseInExpectedReturnOnPlanAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedContributionPlanDisclosureLineItems_019c1be4-a6f0-7353-87fd-77c8a5c5df58" xlink:to="loc_ftre_DefinedBenefitPlanEffectOfOnePercentagePointDecreaseInExpectedReturnOnPlanAssets_aac0cf1e-f9c5-4791-a878-2597e6daadd3" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanExpectedFutureEmployerContributionsNextFiscalYear_73308328-4f05-493d-b5b9-342061f99d1b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanExpectedFutureEmployerContributionsNextFiscalYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedContributionPlanDisclosureLineItems_019c1be4-a6f0-7353-87fd-77c8a5c5df58" xlink:to="loc_us-gaap_DefinedBenefitPlanExpectedFutureEmployerContributionsNextFiscalYear_73308328-4f05-493d-b5b9-342061f99d1b" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fortrea.com/role/PENSIONANDPOSTRETIREMENTPLANSScheduleofNetFundedStatusDetails" xlink:type="simple" xlink:href="ftre-20251231.xsd#PENSIONANDPOSTRETIREMENTPLANSScheduleofNetFundedStatusDetails"/>
  <link:definitionLink xlink:role="http://www.fortrea.com/role/PENSIONANDPOSTRETIREMENTPLANSScheduleofNetFundedStatusDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_504ab75a-7a11-42a0-8151-06f8bce6eeed" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanDisclosureLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_ed0b2522-4381-4740-9256-23ad745342b1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_504ab75a-7a11-42a0-8151-06f8bce6eeed" xlink:to="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_ed0b2522-4381-4740-9256-23ad745342b1" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationAxis_e8389072-2fc6-4be6-a940-b438e84020fe" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BalanceSheetLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_ed0b2522-4381-4740-9256-23ad745342b1" xlink:to="loc_us-gaap_BalanceSheetLocationAxis_e8389072-2fc6-4be6-a940-b438e84020fe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_e8389072-2fc6-4be6-a940-b438e84020fe_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_e8389072-2fc6-4be6-a940-b438e84020fe" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_e8389072-2fc6-4be6-a940-b438e84020fe_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_e323efa8-6665-49f7-914d-a6c74aeceda5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BalanceSheetLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_e8389072-2fc6-4be6-a940-b438e84020fe" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_e323efa8-6665-49f7-914d-a6c74aeceda5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsMember_6205a013-d66a-42a6-a655-613272a4fda8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_e323efa8-6665-49f7-914d-a6c74aeceda5" xlink:to="loc_us-gaap_OtherAssetsMember_6205a013-d66a-42a6-a655-613272a4fda8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesMember_a84d1b06-5595-4659-9f33-29f47101fa07" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherLiabilitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_e323efa8-6665-49f7-914d-a6c74aeceda5" xlink:to="loc_us-gaap_OtherLiabilitiesMember_a84d1b06-5595-4659-9f33-29f47101fa07" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanFundedStatusOfPlan_3497f578-d292-4c0f-bbf0-9cd22e6101b9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanFundedStatusOfPlan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_504ab75a-7a11-42a0-8151-06f8bce6eeed" xlink:to="loc_us-gaap_DefinedBenefitPlanFundedStatusOfPlan_3497f578-d292-4c0f-bbf0-9cd22e6101b9" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fortrea.com/role/PENSIONANDPOSTRETIREMENTPLANSScheduleofAllocationofPlanAssetsDetails" xlink:type="simple" xlink:href="ftre-20251231.xsd#PENSIONANDPOSTRETIREMENTPLANSScheduleofAllocationofPlanAssetsDetails"/>
  <link:definitionLink xlink:role="http://www.fortrea.com/role/PENSIONANDPOSTRETIREMENTPLANSScheduleofAllocationofPlanAssetsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_0a8aa278-c480-4115-9817-50729d4a9207" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanDisclosureLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_edc13db6-effc-41c1-9941-ec9eb29ffbeb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_0a8aa278-c480-4115-9817-50729d4a9207" xlink:to="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_edc13db6-effc-41c1-9941-ec9eb29ffbeb" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis_7564444b-6d15-489e-b19f-69ee8f678c99" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_edc13db6-effc-41c1-9941-ec9eb29ffbeb" xlink:to="loc_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis_7564444b-6d15-489e-b19f-69ee8f678c99" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanAssetCategoriesDomain_7564444b-6d15-489e-b19f-69ee8f678c99_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanAssetCategoriesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis_7564444b-6d15-489e-b19f-69ee8f678c99" xlink:to="loc_us-gaap_PlanAssetCategoriesDomain_7564444b-6d15-489e-b19f-69ee8f678c99_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanAssetCategoriesDomain_c71150e3-132f-448b-94ab-fdab53198b53" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanAssetCategoriesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis_7564444b-6d15-489e-b19f-69ee8f678c99" xlink:to="loc_us-gaap_PlanAssetCategoriesDomain_c71150e3-132f-448b-94ab-fdab53198b53" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanCashAndCashEquivalentsMember_3544edca-8156-4b49-a056-49433c1690cb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanAssetCategoriesDomain_c71150e3-132f-448b-94ab-fdab53198b53" xlink:to="loc_us-gaap_DefinedBenefitPlanCashAndCashEquivalentsMember_3544edca-8156-4b49-a056-49433c1690cb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_DefinedBenefitPlanAnnuitiesMember_1d13387d-dc9b-49bc-b533-8da113ecbd0e" xlink:href="ftre-20251231.xsd#ftre_DefinedBenefitPlanAnnuitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanAssetCategoriesDomain_c71150e3-132f-448b-94ab-fdab53198b53" xlink:to="loc_ftre_DefinedBenefitPlanAnnuitiesMember_1d13387d-dc9b-49bc-b533-8da113ecbd0e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MutualFundMember_8ce537f3-5b35-499e-8e60-109a62c0745a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MutualFundMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanAssetCategoriesDomain_c71150e3-132f-448b-94ab-fdab53198b53" xlink:to="loc_us-gaap_MutualFundMember_8ce537f3-5b35-499e-8e60-109a62c0745a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_1003ddd8-c43e-4123-8cb7-c686feb76e02" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_edc13db6-effc-41c1-9941-ec9eb29ffbeb" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_1003ddd8-c43e-4123-8cb7-c686feb76e02" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_1003ddd8-c43e-4123-8cb7-c686feb76e02_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_1003ddd8-c43e-4123-8cb7-c686feb76e02" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_1003ddd8-c43e-4123-8cb7-c686feb76e02_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_c56db6e4-a9a2-4968-8c96-67d60032b57d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_1003ddd8-c43e-4123-8cb7-c686feb76e02" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_c56db6e4-a9a2-4968-8c96-67d60032b57d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel12And3Member_34e18533-6863-44b6-a179-4b759d491321" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel12And3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_c56db6e4-a9a2-4968-8c96-67d60032b57d" xlink:to="loc_us-gaap_FairValueInputsLevel12And3Member_34e18533-6863-44b6-a179-4b759d491321" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_7424f5fb-3cce-4c5b-8225-a78ce5e0d486" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueInputsLevel12And3Member_34e18533-6863-44b6-a179-4b759d491321" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_7424f5fb-3cce-4c5b-8225-a78ce5e0d486" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_82431b50-40f2-4700-a65b-f6b95ed8b4a2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueInputsLevel12And3Member_34e18533-6863-44b6-a179-4b759d491321" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_82431b50-40f2-4700-a65b-f6b95ed8b4a2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasuredAtNetAssetValuePerShareMember_8e933b53-bb5c-4a23-84c7-3929cfd8ab55" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasuredAtNetAssetValuePerShareMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_c56db6e4-a9a2-4968-8c96-67d60032b57d" xlink:to="loc_us-gaap_FairValueMeasuredAtNetAssetValuePerShareMember_8e933b53-bb5c-4a23-84c7-3929cfd8ab55" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanFairValueOfPlanAssets_a6528c09-31fd-4953-8aba-c874180299d2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanFairValueOfPlanAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_0a8aa278-c480-4115-9817-50729d4a9207" xlink:to="loc_us-gaap_DefinedBenefitPlanFairValueOfPlanAssets_a6528c09-31fd-4953-8aba-c874180299d2" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fortrea.com/role/PENSIONANDPOSTRETIREMENTPLANSScheduleofEffectofSignificantUnobservableInputsChangesinPlanAssetsDetails" xlink:type="simple" xlink:href="ftre-20251231.xsd#PENSIONANDPOSTRETIREMENTPLANSScheduleofEffectofSignificantUnobservableInputsChangesinPlanAssetsDetails"/>
  <link:definitionLink xlink:role="http://www.fortrea.com/role/PENSIONANDPOSTRETIREMENTPLANSScheduleofEffectofSignificantUnobservableInputsChangesinPlanAssetsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_0d6b202a-5b13-4768-82d3-a2e40fd7b696" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanDisclosureLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_245211d3-0e1b-460e-b996-75bbda36284c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_0d6b202a-5b13-4768-82d3-a2e40fd7b696" xlink:to="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_245211d3-0e1b-460e-b996-75bbda36284c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_4346898e-eaa9-4658-81ac-2eadb9c33448" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfDefinedBenefitPlansDisclosuresTable_245211d3-0e1b-460e-b996-75bbda36284c" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_4346898e-eaa9-4658-81ac-2eadb9c33448" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_4346898e-eaa9-4658-81ac-2eadb9c33448_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_4346898e-eaa9-4658-81ac-2eadb9c33448" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_4346898e-eaa9-4658-81ac-2eadb9c33448_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_b371f5c2-47cb-4fc0-a9b5-c2054e1da43e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_4346898e-eaa9-4658-81ac-2eadb9c33448" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_b371f5c2-47cb-4fc0-a9b5-c2054e1da43e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_75aba8e9-bb64-4be2-9817-2bdcf3c923db" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_b371f5c2-47cb-4fc0-a9b5-c2054e1da43e" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_75aba8e9-bb64-4be2-9817-2bdcf3c923db" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanChangeInFairValueOfPlanAssetsLevel3ReconciliationRollForward_73d3e3d8-45b8-4f19-a5c0-5dc511be0bfd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanChangeInFairValueOfPlanAssetsLevel3ReconciliationRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanDisclosureLineItems_0d6b202a-5b13-4768-82d3-a2e40fd7b696" xlink:to="loc_us-gaap_DefinedBenefitPlanChangeInFairValueOfPlanAssetsLevel3ReconciliationRollForward_73d3e3d8-45b8-4f19-a5c0-5dc511be0bfd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanFairValueOfPlanAssets_6f274f41-576f-4ff8-8e96-d41e94d73cb3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanFairValueOfPlanAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanChangeInFairValueOfPlanAssetsLevel3ReconciliationRollForward_73d3e3d8-45b8-4f19-a5c0-5dc511be0bfd" xlink:to="loc_us-gaap_DefinedBenefitPlanFairValueOfPlanAssets_6f274f41-576f-4ff8-8e96-d41e94d73cb3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanActualReturnOnPlanAssetsStillHeld_3fa1ff89-0e87-4326-b2fc-c49e5427d382" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanActualReturnOnPlanAssetsStillHeld"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanChangeInFairValueOfPlanAssetsLevel3ReconciliationRollForward_73d3e3d8-45b8-4f19-a5c0-5dc511be0bfd" xlink:to="loc_us-gaap_DefinedBenefitPlanActualReturnOnPlanAssetsStillHeld_3fa1ff89-0e87-4326-b2fc-c49e5427d382" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanFairValueOfPlanAssets_6d02fddd-f7cd-4332-ad8d-02b60a6c14ed" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanFairValueOfPlanAssets"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fortrea.com/role/PENSIONANDPOSTRETIREMENTPLANSScheduleofPlanAssetAllocationDetails" xlink:type="simple" xlink:href="ftre-20251231.xsd#PENSIONANDPOSTRETIREMENTPLANSScheduleofPlanAssetAllocationDetails"/>
  <link:definitionLink xlink:role="http://www.fortrea.com/role/PENSIONANDPOSTRETIREMENTPLANSScheduleofPlanAssetAllocationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanPlanAssetsAllocationLineItems_9a62c52d-f907-4ca7-a2e3-4d20839bfc48" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanPlanAssetsAllocationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanPlanAssetsAllocationTable_a1b758e0-8818-488d-846a-102629edea49" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanPlanAssetsAllocationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DefinedBenefitPlanPlanAssetsAllocationLineItems_9a62c52d-f907-4ca7-a2e3-4d20839bfc48" xlink:to="loc_us-gaap_DefinedBenefitPlanPlanAssetsAllocationTable_a1b758e0-8818-488d-846a-102629edea49" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis_370ad827-18bb-4808-9502-f5b664c7c965" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DefinedBenefitPlanPlanAssetsAllocationTable_a1b758e0-8818-488d-846a-102629edea49" xlink:to="loc_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis_370ad827-18bb-4808-9502-f5b664c7c965" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanAssetCategoriesDomain_370ad827-18bb-4808-9502-f5b664c7c965_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanAssetCategoriesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis_370ad827-18bb-4808-9502-f5b664c7c965" xlink:to="loc_us-gaap_PlanAssetCategoriesDomain_370ad827-18bb-4808-9502-f5b664c7c965_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanAssetCategoriesDomain_8af50801-b3c6-4213-a1a1-7889a59f87ea" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanAssetCategoriesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DefinedBenefitPlanByPlanAssetCategoriesAxis_370ad827-18bb-4808-9502-f5b664c7c965" xlink:to="loc_us-gaap_PlanAssetCategoriesDomain_8af50801-b3c6-4213-a1a1-7889a59f87ea" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanEquitySecuritiesMember_f10c8ad8-00de-408a-8abb-b85640790755" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanEquitySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanAssetCategoriesDomain_8af50801-b3c6-4213-a1a1-7889a59f87ea" xlink:to="loc_us-gaap_DefinedBenefitPlanEquitySecuritiesMember_f10c8ad8-00de-408a-8abb-b85640790755" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanDebtSecurityMember_37d7d4e5-795d-47c6-a76d-83f2f376618a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanDebtSecurityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanAssetCategoriesDomain_8af50801-b3c6-4213-a1a1-7889a59f87ea" xlink:to="loc_us-gaap_DefinedBenefitPlanDebtSecurityMember_37d7d4e5-795d-47c6-a76d-83f2f376618a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FixedAnnuityMember_3b078015-8d3b-4726-ba73-aec1348dbeda" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FixedAnnuityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanAssetCategoriesDomain_8af50801-b3c6-4213-a1a1-7889a59f87ea" xlink:to="loc_us-gaap_FixedAnnuityMember_3b078015-8d3b-4726-ba73-aec1348dbeda" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanRealEstateMember_c2570957-de93-4462-878d-63b25b671100" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanRealEstateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanAssetCategoriesDomain_8af50801-b3c6-4213-a1a1-7889a59f87ea" xlink:to="loc_us-gaap_DefinedBenefitPlanRealEstateMember_c2570957-de93-4462-878d-63b25b671100" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_DefinedBenefitPlanOtherMember_6279c728-2e6e-4a25-827b-345fc5b485be" xlink:href="ftre-20251231.xsd#ftre_DefinedBenefitPlanOtherMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanAssetCategoriesDomain_8af50801-b3c6-4213-a1a1-7889a59f87ea" xlink:to="loc_ftre_DefinedBenefitPlanOtherMember_6279c728-2e6e-4a25-827b-345fc5b485be" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_44271e0d-dabc-44c8-9627-ec9d835d657e" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DefinedBenefitPlanPlanAssetsAllocationTable_a1b758e0-8818-488d-846a-102629edea49" xlink:to="loc_srt_RangeAxis_44271e0d-dabc-44c8-9627-ec9d835d657e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_44271e0d-dabc-44c8-9627-ec9d835d657e_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_44271e0d-dabc-44c8-9627-ec9d835d657e" xlink:to="loc_srt_RangeMember_44271e0d-dabc-44c8-9627-ec9d835d657e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_e678b1f0-6b2d-43ce-a2ad-6a8653da96c0" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_44271e0d-dabc-44c8-9627-ec9d835d657e" xlink:to="loc_srt_RangeMember_e678b1f0-6b2d-43ce-a2ad-6a8653da96c0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_d7b6340c-befe-406f-90de-8c035382ffa9" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_e678b1f0-6b2d-43ce-a2ad-6a8653da96c0" xlink:to="loc_srt_MinimumMember_d7b6340c-befe-406f-90de-8c035382ffa9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_136db31b-463f-407b-bd34-eb4126688e39" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_e678b1f0-6b2d-43ce-a2ad-6a8653da96c0" xlink:to="loc_srt_MaximumMember_136db31b-463f-407b-bd34-eb4126688e39" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations_90953165-aa79-4085-a795-605d62a7145c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanPlanAssetsAllocationLineItems_9a62c52d-f907-4ca7-a2e3-4d20839bfc48" xlink:to="loc_us-gaap_DefinedBenefitPlanWeightedAverageAssetAllocations_90953165-aa79-4085-a795-605d62a7145c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DefinedBenefitPlanPlanAssetsTargetAllocationPercentage_631edbc4-1952-4a4a-94ca-ab9858eebf6f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DefinedBenefitPlanPlanAssetsTargetAllocationPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DefinedBenefitPlanPlanAssetsAllocationLineItems_9a62c52d-f907-4ca7-a2e3-4d20839bfc48" xlink:to="loc_us-gaap_DefinedBenefitPlanPlanAssetsTargetAllocationPercentage_631edbc4-1952-4a4a-94ca-ab9858eebf6f" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fortrea.com/role/TRANSACTIONSWITHFORMERPARENTAllocationofGeneralCorporateandOtherExpensesDetails" xlink:type="simple" xlink:href="ftre-20251231.xsd#TRANSACTIONSWITHFORMERPARENTAllocationofGeneralCorporateandOtherExpensesDetails"/>
  <link:definitionLink xlink:role="http://www.fortrea.com/role/TRANSACTIONSWITHFORMERPARENTAllocationofGeneralCorporateandOtherExpensesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionLineItems_c1dfde74-3397-452b-815d-8d1ba5ed0e49" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_f33dc0b1-62c5-40fa-955f-d089307adb30" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_c1dfde74-3397-452b-815d-8d1ba5ed0e49" xlink:to="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_f33dc0b1-62c5-40fa-955f-d089307adb30" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionAxis_156cd9a7-8b4c-458e-83e5-bdd7540e4e57" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_f33dc0b1-62c5-40fa-955f-d089307adb30" xlink:to="loc_us-gaap_RelatedPartyTransactionAxis_156cd9a7-8b4c-458e-83e5-bdd7540e4e57" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_156cd9a7-8b4c-458e-83e5-bdd7540e4e57_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_156cd9a7-8b4c-458e-83e5-bdd7540e4e57" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_156cd9a7-8b4c-458e-83e5-bdd7540e4e57_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_00d00b4b-8f23-47c1-956a-2b5d74e88ac0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_156cd9a7-8b4c-458e-83e5-bdd7540e4e57" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_00d00b4b-8f23-47c1-956a-2b5d74e88ac0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_DirectCostsRelatedPartyMember_55c08dd8-748c-4016-8f80-a4ce47c0c4d8" xlink:href="ftre-20251231.xsd#ftre_DirectCostsRelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_00d00b4b-8f23-47c1-956a-2b5d74e88ac0" xlink:to="loc_ftre_DirectCostsRelatedPartyMember_55c08dd8-748c-4016-8f80-a4ce47c0c4d8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_SellingGeneralAndAdministrativeExpensesRelatedPartyMember_df8ac545-fea6-4df0-9a2f-0b44c696f99a" xlink:href="ftre-20251231.xsd#ftre_SellingGeneralAndAdministrativeExpensesRelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_00d00b4b-8f23-47c1-956a-2b5d74e88ac0" xlink:to="loc_ftre_SellingGeneralAndAdministrativeExpensesRelatedPartyMember_df8ac545-fea6-4df0-9a2f-0b44c696f99a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_RestructuringAndOtherChargesRelatedPartyMember_4ab757fc-bc8c-430e-a764-67ff7813a552" xlink:href="ftre-20251231.xsd#ftre_RestructuringAndOtherChargesRelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_00d00b4b-8f23-47c1-956a-2b5d74e88ac0" xlink:to="loc_ftre_RestructuringAndOtherChargesRelatedPartyMember_4ab757fc-bc8c-430e-a764-67ff7813a552" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_ForeignExchangeGainLossRelatedPartyMember_c889d0dd-209a-49fd-bde8-ba500cc54711" xlink:href="ftre-20251231.xsd#ftre_ForeignExchangeGainLossRelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_00d00b4b-8f23-47c1-956a-2b5d74e88ac0" xlink:to="loc_ftre_ForeignExchangeGainLossRelatedPartyMember_c889d0dd-209a-49fd-bde8-ba500cc54711" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionAmountsOfTransaction_2820c6d5-150a-4288-8a9f-436737c924fe" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionAmountsOfTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_c1dfde74-3397-452b-815d-8d1ba5ed0e49" xlink:to="loc_us-gaap_RelatedPartyTransactionAmountsOfTransaction_2820c6d5-150a-4288-8a9f-436737c924fe" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fortrea.com/role/TRANSACTIONSWITHFORMERPARENTNarrativeDetails" xlink:type="simple" xlink:href="ftre-20251231.xsd#TRANSACTIONSWITHFORMERPARENTNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.fortrea.com/role/TRANSACTIONSWITHFORMERPARENTNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionLineItems_dcd47856-ebf3-421a-ad90-f5c3635aa447" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_2f7f9af4-c669-43ab-882a-6dfebcf1cbb9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_dcd47856-ebf3-421a-ad90-f5c3635aa447" xlink:to="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_2f7f9af4-c669-43ab-882a-6dfebcf1cbb9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionAxis_31712638-5ed2-4150-8740-cfff7ac1265d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_2f7f9af4-c669-43ab-882a-6dfebcf1cbb9" xlink:to="loc_us-gaap_RelatedPartyTransactionAxis_31712638-5ed2-4150-8740-cfff7ac1265d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_31712638-5ed2-4150-8740-cfff7ac1265d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_31712638-5ed2-4150-8740-cfff7ac1265d" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_31712638-5ed2-4150-8740-cfff7ac1265d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_062fdbc1-7c56-4c8e-964d-e0a375fdb12a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_31712638-5ed2-4150-8740-cfff7ac1265d" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_062fdbc1-7c56-4c8e-964d-e0a375fdb12a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_GeneralFinancingActivitiesMember_ffc198db-e263-4a60-8c95-63e66d8f1483" xlink:href="ftre-20251231.xsd#ftre_GeneralFinancingActivitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_062fdbc1-7c56-4c8e-964d-e0a375fdb12a" xlink:to="loc_ftre_GeneralFinancingActivitiesMember_ffc198db-e263-4a60-8c95-63e66d8f1483" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_CorporateAllocationsMember_bd4f1d04-11e7-43d7-8d58-58e1eeda7b8b" xlink:href="ftre-20251231.xsd#ftre_CorporateAllocationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_062fdbc1-7c56-4c8e-964d-e0a375fdb12a" xlink:to="loc_ftre_CorporateAllocationsMember_bd4f1d04-11e7-43d7-8d58-58e1eeda7b8b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_SubcontractServicesMember_2e8be678-05d2-4579-bc95-35bea266a190" xlink:href="ftre-20251231.xsd#ftre_SubcontractServicesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_062fdbc1-7c56-4c8e-964d-e0a375fdb12a" xlink:to="loc_ftre_SubcontractServicesMember_2e8be678-05d2-4579-bc95-35bea266a190" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionAmountsOfTransaction_bc4d2dff-8719-44bc-b68a-d28d9a1a5928" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionAmountsOfTransaction"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_dcd47856-ebf3-421a-ad90-f5c3635aa447" xlink:to="loc_us-gaap_RelatedPartyTransactionAmountsOfTransaction_bc4d2dff-8719-44bc-b68a-d28d9a1a5928" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fortrea.com/role/TRANSACTIONSWITHFORMERPARENTNetTransfersToandFromLabcorpDetails" xlink:type="simple" xlink:href="ftre-20251231.xsd#TRANSACTIONSWITHFORMERPARENTNetTransfersToandFromLabcorpDetails"/>
  <link:definitionLink xlink:role="http://www.fortrea.com/role/TRANSACTIONSWITHFORMERPARENTNetTransfersToandFromLabcorpDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionLineItems_b577327c-b957-4ef0-8b51-4cdd6287d335" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_36b66777-0785-4089-8300-65620515a53a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_b577327c-b957-4ef0-8b51-4cdd6287d335" xlink:to="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_36b66777-0785-4089-8300-65620515a53a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_860b6ac7-c489-493f-a8db-466245e9122a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_36b66777-0785-4089-8300-65620515a53a" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_860b6ac7-c489-493f-a8db-466245e9122a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_860b6ac7-c489-493f-a8db-466245e9122a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_860b6ac7-c489-493f-a8db-466245e9122a" xlink:to="loc_us-gaap_RelatedPartyDomain_860b6ac7-c489-493f-a8db-466245e9122a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_b57b7490-31ce-46a7-bc65-d2e220483d6a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_860b6ac7-c489-493f-a8db-466245e9122a" xlink:to="loc_us-gaap_RelatedPartyDomain_b57b7490-31ce-46a7-bc65-d2e220483d6a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyMember_bf530191-b215-4fcf-a462-d0a3f26f262b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_b57b7490-31ce-46a7-bc65-d2e220483d6a" xlink:to="loc_us-gaap_RelatedPartyMember_bf530191-b215-4fcf-a462-d0a3f26f262b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionAxis_f498e26f-332c-4d79-b6e9-3a051aecb36b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_36b66777-0785-4089-8300-65620515a53a" xlink:to="loc_us-gaap_RelatedPartyTransactionAxis_f498e26f-332c-4d79-b6e9-3a051aecb36b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_f498e26f-332c-4d79-b6e9-3a051aecb36b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_f498e26f-332c-4d79-b6e9-3a051aecb36b" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_f498e26f-332c-4d79-b6e9-3a051aecb36b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_5fcc967e-b43d-48a1-abb7-bd072991bf61" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_f498e26f-332c-4d79-b6e9-3a051aecb36b" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_5fcc967e-b43d-48a1-abb7-bd072991bf61" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_SpecialPaymentToFormerParentMember_2f434902-82e9-484d-b624-74cfe495eb3d" xlink:href="ftre-20251231.xsd#ftre_SpecialPaymentToFormerParentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_5fcc967e-b43d-48a1-abb7-bd072991bf61" xlink:to="loc_ftre_SpecialPaymentToFormerParentMember_2f434902-82e9-484d-b624-74cfe495eb3d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_GeneralFinancingActivitiesMember_14e92d16-a3b4-44b4-919d-5c0047fac847" xlink:href="ftre-20251231.xsd#ftre_GeneralFinancingActivitiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_5fcc967e-b43d-48a1-abb7-bd072991bf61" xlink:to="loc_ftre_GeneralFinancingActivitiesMember_14e92d16-a3b4-44b4-919d-5c0047fac847" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_CorporateAllocationsMember_e8d1e546-cce9-46e9-b4a5-9baa331d3868" xlink:href="ftre-20251231.xsd#ftre_CorporateAllocationsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_5fcc967e-b43d-48a1-abb7-bd072991bf61" xlink:to="loc_ftre_CorporateAllocationsMember_e8d1e546-cce9-46e9-b4a5-9baa331d3868" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_StockCompensationExpenseMember_3bb11fa0-277f-4193-9961-62c57b2dabb0" xlink:href="ftre-20251231.xsd#ftre_StockCompensationExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_5fcc967e-b43d-48a1-abb7-bd072991bf61" xlink:to="loc_ftre_StockCompensationExpenseMember_3bb11fa0-277f-4193-9961-62c57b2dabb0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_NetTransfersFromToParent_70db21bc-a1f9-48e4-b164-e43a8b9eea60" xlink:href="ftre-20251231.xsd#ftre_NetTransfersFromToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_b577327c-b957-4ef0-8b51-4cdd6287d335" xlink:to="loc_ftre_NetTransfersFromToParent_70db21bc-a1f9-48e4-b164-e43a8b9eea60" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.fortrea.com/role/BUSINESSSEGMENTINFORMATIONScheduleofSegmentReportingInformationDetails" xlink:type="simple" xlink:href="ftre-20251231.xsd#BUSINESSSEGMENTINFORMATIONScheduleofSegmentReportingInformationDetails"/>
  <link:definitionLink xlink:role="http://www.fortrea.com/role/BUSINESSSEGMENTINFORMATIONScheduleofSegmentReportingInformationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_b43a9826-849b-433d-a982-c642f8603339" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentReportingInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_dd2cf97a-c9fb-433b-b02e-bf320f93bd80" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_b43a9826-849b-433d-a982-c642f8603339" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_dd2cf97a-c9fb-433b-b02e-bf320f93bd80" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_92b1018e-804b-4bf2-ba60-1453def89297" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_dd2cf97a-c9fb-433b-b02e-bf320f93bd80" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_92b1018e-804b-4bf2-ba60-1453def89297" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_92b1018e-804b-4bf2-ba60-1453def89297_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_92b1018e-804b-4bf2-ba60-1453def89297" xlink:to="loc_us-gaap_SegmentDomain_92b1018e-804b-4bf2-ba60-1453def89297_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_f2fee0b1-d55b-4f03-842b-c394a54dc957" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_92b1018e-804b-4bf2-ba60-1453def89297" xlink:to="loc_us-gaap_SegmentDomain_f2fee0b1-d55b-4f03-842b-c394a54dc957" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_ClinicalServicesSegmentMember_25eb6c07-77b0-4755-b7bc-abf6993a96c8" xlink:href="ftre-20251231.xsd#ftre_ClinicalServicesSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_f2fee0b1-d55b-4f03-842b-c394a54dc957" xlink:to="loc_ftre_ClinicalServicesSegmentMember_25eb6c07-77b0-4755-b7bc-abf6993a96c8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsAxis_dfc6029d-03fa-4ed4-ade6-2bd6b417f9ab" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_dd2cf97a-c9fb-433b-b02e-bf320f93bd80" xlink:to="loc_srt_ConsolidationItemsAxis_dfc6029d-03fa-4ed4-ade6-2bd6b417f9ab" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_dfc6029d-03fa-4ed4-ade6-2bd6b417f9ab_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ConsolidationItemsAxis_dfc6029d-03fa-4ed4-ade6-2bd6b417f9ab" xlink:to="loc_srt_ConsolidationItemsDomain_dfc6029d-03fa-4ed4-ade6-2bd6b417f9ab_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ConsolidationItemsDomain_7b2a7da4-e7c7-4ff6-a294-2ad44e3cf7dc" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ConsolidationItemsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ConsolidationItemsAxis_dfc6029d-03fa-4ed4-ade6-2bd6b417f9ab" xlink:to="loc_srt_ConsolidationItemsDomain_7b2a7da4-e7c7-4ff6-a294-2ad44e3cf7dc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingSegmentsMember_9a93f777-7db4-4183-8c8e-60223cd07fa2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingSegmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_7b2a7da4-e7c7-4ff6-a294-2ad44e3cf7dc" xlink:to="loc_us-gaap_OperatingSegmentsMember_9a93f777-7db4-4183-8c8e-60223cd07fa2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateNonSegmentMember_4f252bf8-e025-42cc-bf64-df4e02c50bae" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CorporateNonSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ConsolidationItemsDomain_7b2a7da4-e7c7-4ff6-a294-2ad44e3cf7dc" xlink:to="loc_us-gaap_CorporateNonSegmentMember_4f252bf8-e025-42cc-bf64-df4e02c50bae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_5251a118-624c-44e3-b723-de0cc4797cca" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_b43a9826-849b-433d-a982-c642f8603339" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_5251a118-624c-44e3-b723-de0cc4797cca" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingCostsAndExpenses_70071a56-b302-4793-901f-650536027369" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingCostsAndExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_b43a9826-849b-433d-a982-c642f8603339" xlink:to="loc_us-gaap_OperatingCostsAndExpenses_70071a56-b302-4793-901f-650536027369" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServiceExcludingDepreciationDepletionAndAmortization_48e89f4d-408b-4479-a858-ebcf074c5721" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CostOfGoodsAndServiceExcludingDepreciationDepletionAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_b43a9826-849b-433d-a982-c642f8603339" xlink:to="loc_us-gaap_CostOfGoodsAndServiceExcludingDepreciationDepletionAndAmortization_48e89f4d-408b-4479-a858-ebcf074c5721" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingGeneralAndAdministrativeExpense_7bf62450-93f0-4247-9303-a35a303eab13" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SellingGeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_b43a9826-849b-433d-a982-c642f8603339" xlink:to="loc_us-gaap_SellingGeneralAndAdministrativeExpense_7bf62450-93f0-4247-9303-a35a303eab13" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationAndAmortization_c4da9409-1ba4-4ce6-ae44-b26eeb2eef46" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_b43a9826-849b-433d-a982-c642f8603339" xlink:to="loc_us-gaap_DepreciationAndAmortization_c4da9409-1ba4-4ce6-ae44-b26eeb2eef46" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_SegmentOperatingIncomeLoss_00e1fab5-7503-4cc7-876f-aad86ae2e2ca" xlink:href="ftre-20251231.xsd#ftre_SegmentOperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_b43a9826-849b-433d-a982-c642f8603339" xlink:to="loc_ftre_SegmentOperatingIncomeLoss_00e1fab5-7503-4cc7-876f-aad86ae2e2ca" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCostAndExpenseOperating_4ee60695-e353-4987-8d60-706cf5adcc16" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherCostAndExpenseOperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_b43a9826-849b-433d-a982-c642f8603339" xlink:to="loc_us-gaap_OtherCostAndExpenseOperating_4ee60695-e353-4987-8d60-706cf5adcc16" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentForAmortization_4d860aaa-e086-4891-ad50-be82347bbd7c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdjustmentForAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_b43a9826-849b-433d-a982-c642f8603339" xlink:to="loc_us-gaap_AdjustmentForAmortization_4d860aaa-e086-4891-ad50-be82347bbd7c" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillAndIntangibleAssetImpairment_3ad4c228-b414-4b40-9153-2667802357c9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GoodwillAndIntangibleAssetImpairment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_b43a9826-849b-433d-a982-c642f8603339" xlink:to="loc_us-gaap_GoodwillAndIntangibleAssetImpairment_3ad4c228-b414-4b40-9153-2667802357c9" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestructuringAndRelatedCostIncurredCost_95c4c21b-594e-44ff-a517-a2b27add4706" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestructuringAndRelatedCostIncurredCost"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_b43a9826-849b-433d-a982-c642f8603339" xlink:to="loc_us-gaap_RestructuringAndRelatedCostIncurredCost_95c4c21b-594e-44ff-a517-a2b27add4706" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_6aa7c009-0318-4b35-b163-631fd4b4d815" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_b43a9826-849b-433d-a982-c642f8603339" xlink:to="loc_us-gaap_OperatingIncomeLoss_6aa7c009-0318-4b35-b163-631fd4b4d815" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestIncomeExpenseNonoperatingNet_6ebd4a6c-755a-461f-aab4-09104abcc33c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestIncomeExpenseNonoperatingNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_b43a9826-849b-433d-a982-c642f8603339" xlink:to="loc_us-gaap_InterestIncomeExpenseNonoperatingNet_6ebd4a6c-755a-461f-aab4-09104abcc33c" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ForeignCurrencyTransactionGainLossBeforeTax_4cf2d85c-2d9e-4fbe-8a3c-1dda5ef26a83" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ForeignCurrencyTransactionGainLossBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_b43a9826-849b-433d-a982-c642f8603339" xlink:to="loc_us-gaap_ForeignCurrencyTransactionGainLossBeforeTax_4cf2d85c-2d9e-4fbe-8a3c-1dda5ef26a83" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_6140ec8b-fde6-4013-b8d6-042c21fb552f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherNonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_b43a9826-849b-433d-a982-c642f8603339" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_6140ec8b-fde6-4013-b8d6-042c21fb552f" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_2d8d0ef0-5679-4ba6-aec6-ea43a1091f0b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_b43a9826-849b-433d-a982-c642f8603339" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_2d8d0ef0-5679-4ba6-aec6-ea43a1091f0b" xlink:type="arc" order="14"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://fasb.org/us-gaap/role/eedm/ExtensibleEnumerationLists" xlink:type="simple" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-roles-2025.xsd#eedm"/>
  <link:definitionLink xlink:role="http://fasb.org/us-gaap/role/eedm/ExtensibleEnumerationLists" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementAbstract"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillAndIntangibleAssetImpairment" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GoodwillAndIntangibleAssetImpairment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementAbstract" xlink:to="loc_us-gaap_GoodwillAndIntangibleAssetImpairment" xlink:type="arc" order="691"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedLiabilitiesCurrent" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccruedLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementAbstract" xlink:to="loc_us-gaap_AccruedLiabilitiesCurrent" xlink:type="arc" order="692"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetsAbstract"/>
    <link:loc xlink:type="locator" xlink:label="loc_ftre_PropertyPlantAndEquipmentAndOperatingLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization_935cb89e-8dfb-4ebc-bc83-66ebaa27d518" xlink:href="ftre-20251231.xsd#ftre_PropertyPlantAndEquipmentAndOperatingLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract" xlink:to="loc_ftre_PropertyPlantAndEquipmentAndOperatingLeaseRightOfUseAssetAfterAccumulatedDepreciationAndAmortization_935cb89e-8dfb-4ebc-bc83-66ebaa27d518" xlink:type="arc" order="101"/>
  </link:definitionLink>
</link:linkbase>
