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

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019e18cb-a38e-75ad-9146-a848932bba60,g:e04b20cb-32d6-4807-a503-314cd71daeed-->
<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.opploans.com/role/CoverPage" xlink:type="simple" xlink:href="opfi-20260609.xsd#CoverPage"/>
  <link:definitionLink xlink:role="http://www.opploans.com/role/CoverPage" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationLineItems_019e18cb-a38e-7fe9-9eda-080efc25d15e" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_DocumentInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationTable_019e18cb-a38e-74b0-9599-6b90fd2eafca" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_DocumentInformationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_DocumentInformationLineItems_019e18cb-a38e-7fe9-9eda-080efc25d15e" xlink:to="loc_dei_DocumentInformationTable_019e18cb-a38e-74b0-9599-6b90fd2eafca" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019e18cb-a38e-7129-941d-7db0aec053f4" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_DocumentInformationTable_019e18cb-a38e-74b0-9599-6b90fd2eafca" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019e18cb-a38e-7129-941d-7db0aec053f4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019e18cb-a38e-7129-941d-7db0aec053f4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019e18cb-a38e-7129-941d-7db0aec053f4" xlink:to="loc_us-gaap_ClassOfStockDomain_019e18cb-a38e-7129-941d-7db0aec053f4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019e18cb-a38e-790a-bf84-4251dd9bf2ca" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019e18cb-a38e-7129-941d-7db0aec053f4" xlink:to="loc_us-gaap_ClassOfStockDomain_019e18cb-a38e-790a-bf84-4251dd9bf2ca" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_019e18cb-a38e-7c65-9272-aa1769a8915e" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019e18cb-a38e-790a-bf84-4251dd9bf2ca" xlink:to="loc_us-gaap_CommonClassAMember_019e18cb-a38e-7c65-9272-aa1769a8915e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantMember_019e18cb-a38e-7173-a2d9-e36f8a007b03" xlink:href="https://xbrl.fasb.org/us-gaap/2024/elts/us-gaap-2024.xsd#us-gaap_WarrantMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019e18cb-a38e-790a-bf84-4251dd9bf2ca" xlink:to="loc_us-gaap_WarrantMember_019e18cb-a38e-7173-a2d9-e36f8a007b03" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_019e18cb-a38e-74b6-9626-1b9008f36c2c" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_DocumentType"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019e18cb-a38e-7fe9-9eda-080efc25d15e" xlink:to="loc_dei_DocumentType_019e18cb-a38e-74b6-9626-1b9008f36c2c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_019e18cb-a38e-7cea-9a3d-c8529c5d8716" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_DocumentPeriodEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019e18cb-a38e-7fe9-9eda-080efc25d15e" xlink:to="loc_dei_DocumentPeriodEndDate_019e18cb-a38e-7cea-9a3d-c8529c5d8716" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_019e18cb-a38e-775f-8fa5-f6ed7d5cf9e9" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityRegistrantName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019e18cb-a38e-7fe9-9eda-080efc25d15e" xlink:to="loc_dei_EntityRegistrantName_019e18cb-a38e-775f-8fa5-f6ed7d5cf9e9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_019e18cb-a38e-740f-9342-b23d17f3823a" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityIncorporationStateCountryCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019e18cb-a38e-7fe9-9eda-080efc25d15e" xlink:to="loc_dei_EntityIncorporationStateCountryCode_019e18cb-a38e-740f-9342-b23d17f3823a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_019e18cb-a38e-7e35-80ab-45e288c8f765" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityFileNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019e18cb-a38e-7fe9-9eda-080efc25d15e" xlink:to="loc_dei_EntityFileNumber_019e18cb-a38e-7e35-80ab-45e288c8f765" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_019e18cb-a38e-7850-b188-f788058d7d3d" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityTaxIdentificationNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019e18cb-a38e-7fe9-9eda-080efc25d15e" xlink:to="loc_dei_EntityTaxIdentificationNumber_019e18cb-a38e-7850-b188-f788058d7d3d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_019e18cb-a38e-754e-a743-634b64c6188d" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityAddressAddressLine1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019e18cb-a38e-7fe9-9eda-080efc25d15e" xlink:to="loc_dei_EntityAddressAddressLine1_019e18cb-a38e-754e-a743-634b64c6188d" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine2_019e18cb-a38e-7245-af74-3116bf971683" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityAddressAddressLine2"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019e18cb-a38e-7fe9-9eda-080efc25d15e" xlink:to="loc_dei_EntityAddressAddressLine2_019e18cb-a38e-7245-af74-3116bf971683" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_019e18cb-a38e-77c9-96f7-291758bdd67f" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityAddressCityOrTown"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019e18cb-a38e-7fe9-9eda-080efc25d15e" xlink:to="loc_dei_EntityAddressCityOrTown_019e18cb-a38e-77c9-96f7-291758bdd67f" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_019e18cb-a38e-7873-825e-70c4406f4f68" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityAddressStateOrProvince"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019e18cb-a38e-7fe9-9eda-080efc25d15e" xlink:to="loc_dei_EntityAddressStateOrProvince_019e18cb-a38e-7873-825e-70c4406f4f68" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_019e18cb-a38e-7c97-a21c-5e194e6257f8" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityAddressPostalZipCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019e18cb-a38e-7fe9-9eda-080efc25d15e" xlink:to="loc_dei_EntityAddressPostalZipCode_019e18cb-a38e-7c97-a21c-5e194e6257f8" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_019e18cb-a38e-7430-aaf8-37fa65ad6446" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_CityAreaCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019e18cb-a38e-7fe9-9eda-080efc25d15e" xlink:to="loc_dei_CityAreaCode_019e18cb-a38e-7430-aaf8-37fa65ad6446" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_019e18cb-a38e-7cb7-88cd-00845247a8bf" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_LocalPhoneNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019e18cb-a38e-7fe9-9eda-080efc25d15e" xlink:to="loc_dei_LocalPhoneNumber_019e18cb-a38e-7cb7-88cd-00845247a8bf" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_WrittenCommunications_019e18cb-a38e-70b6-9f62-c0f035d12685" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_WrittenCommunications"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019e18cb-a38e-7fe9-9eda-080efc25d15e" xlink:to="loc_dei_WrittenCommunications_019e18cb-a38e-70b6-9f62-c0f035d12685" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SolicitingMaterial_019e18cb-a38e-7e84-af59-8766e8b791c4" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_SolicitingMaterial"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019e18cb-a38e-7fe9-9eda-080efc25d15e" xlink:to="loc_dei_SolicitingMaterial_019e18cb-a38e-7e84-af59-8766e8b791c4" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_PreCommencementTenderOffer_019e18cb-a38e-7aaf-bc9b-5bba33953798" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_PreCommencementTenderOffer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019e18cb-a38e-7fe9-9eda-080efc25d15e" xlink:to="loc_dei_PreCommencementTenderOffer_019e18cb-a38e-7aaf-bc9b-5bba33953798" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_PreCommencementIssuerTenderOffer_019e18cb-a38e-709c-afa1-a0086b898537" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_PreCommencementIssuerTenderOffer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019e18cb-a38e-7fe9-9eda-080efc25d15e" xlink:to="loc_dei_PreCommencementIssuerTenderOffer_019e18cb-a38e-709c-afa1-a0086b898537" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_019e18cb-a38e-716c-94e3-84e10f397b39" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_Security12bTitle"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019e18cb-a38e-7fe9-9eda-080efc25d15e" xlink:to="loc_dei_Security12bTitle_019e18cb-a38e-716c-94e3-84e10f397b39" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_019e18cb-a38e-7aec-b085-0d530cb27baa" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_TradingSymbol"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019e18cb-a38e-7fe9-9eda-080efc25d15e" xlink:to="loc_dei_TradingSymbol_019e18cb-a38e-7aec-b085-0d530cb27baa" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_019e18cb-a38e-7bf1-8a27-d1ac0bdfc2df" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_SecurityExchangeName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019e18cb-a38e-7fe9-9eda-080efc25d15e" xlink:to="loc_dei_SecurityExchangeName_019e18cb-a38e-7bf1-8a27-d1ac0bdfc2df" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_019e18cb-a38e-7cdf-a399-f48d200a2bde" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityEmergingGrowthCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019e18cb-a38e-7fe9-9eda-080efc25d15e" xlink:to="loc_dei_EntityEmergingGrowthCompany_019e18cb-a38e-7cdf-a399-f48d200a2bde" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityExTransitionPeriod_019e18cb-a38e-76ba-a6db-2dc10312d5e8" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityExTransitionPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019e18cb-a38e-7fe9-9eda-080efc25d15e" xlink:to="loc_dei_EntityExTransitionPeriod_019e18cb-a38e-76ba-a6db-2dc10312d5e8" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_019e18cb-a38e-7f2f-ac65-9cc685eb76ef" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_EntityCentralIndexKey"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019e18cb-a38e-7fe9-9eda-080efc25d15e" xlink:to="loc_dei_EntityCentralIndexKey_019e18cb-a38e-7f2f-ac65-9cc685eb76ef" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_019e18cb-a38e-7f72-b3fc-36b7f78b93b4" xlink:href="https://xbrl.sec.gov/dei/2024/dei-2024.xsd#dei_AmendmentFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019e18cb-a38e-7fe9-9eda-080efc25d15e" xlink:to="loc_dei_AmendmentFlag_019e18cb-a38e-7f72-b3fc-36b7f78b93b4" xlink:type="arc" order="23"/>
  </link:definitionLink>
</link:linkbase>
