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

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019ecc6e-8898-7b45-847b-303ba6e086d6,g:855d90ab-5504-48c0-b67b-0beb06bb3b7e-->
<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-20260616.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_019ecc6e-8898-71fb-a935-5a25b5c7d175" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_DocumentInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationTable_019ecc6e-8898-76e5-9098-a122a4b27a15" 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_019ecc6e-8898-71fb-a935-5a25b5c7d175" xlink:to="loc_dei_DocumentInformationTable_019ecc6e-8898-76e5-9098-a122a4b27a15" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019ecc6e-8898-7ee0-a743-58a20c7a68f1" 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_019ecc6e-8898-76e5-9098-a122a4b27a15" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019ecc6e-8898-7ee0-a743-58a20c7a68f1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019ecc6e-8898-7ee0-a743-58a20c7a68f1_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_019ecc6e-8898-7ee0-a743-58a20c7a68f1" xlink:to="loc_us-gaap_ClassOfStockDomain_019ecc6e-8898-7ee0-a743-58a20c7a68f1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019ecc6e-8898-7f81-a9c6-3b2916321ee5" 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_019ecc6e-8898-7ee0-a743-58a20c7a68f1" xlink:to="loc_us-gaap_ClassOfStockDomain_019ecc6e-8898-7f81-a9c6-3b2916321ee5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_019ecc6e-8898-78fe-8b8e-3c2b0b890cfd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019ecc6e-8898-7f81-a9c6-3b2916321ee5" xlink:to="loc_us-gaap_CommonClassAMember_019ecc6e-8898-78fe-8b8e-3c2b0b890cfd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantMember_019ecc6e-8898-781b-8c47-eb17dbe910a0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_WarrantMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019ecc6e-8898-7f81-a9c6-3b2916321ee5" xlink:to="loc_us-gaap_WarrantMember_019ecc6e-8898-781b-8c47-eb17dbe910a0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_019ecc6e-8898-7c22-87f4-3401986f5d23" 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_019ecc6e-8898-71fb-a935-5a25b5c7d175" xlink:to="loc_dei_DocumentType_019ecc6e-8898-7c22-87f4-3401986f5d23" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_019ecc6e-8898-7257-a624-f730274def83" 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_019ecc6e-8898-71fb-a935-5a25b5c7d175" xlink:to="loc_dei_DocumentPeriodEndDate_019ecc6e-8898-7257-a624-f730274def83" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_019ecc6e-8898-73e6-ba68-c48279f1273e" 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_019ecc6e-8898-71fb-a935-5a25b5c7d175" xlink:to="loc_dei_EntityRegistrantName_019ecc6e-8898-73e6-ba68-c48279f1273e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_019ecc6e-8898-7ccc-bbe2-3f33fb511425" 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_019ecc6e-8898-71fb-a935-5a25b5c7d175" xlink:to="loc_dei_EntityIncorporationStateCountryCode_019ecc6e-8898-7ccc-bbe2-3f33fb511425" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_019ecc6e-8898-7684-82ca-c162360ce9f0" 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_019ecc6e-8898-71fb-a935-5a25b5c7d175" xlink:to="loc_dei_EntityFileNumber_019ecc6e-8898-7684-82ca-c162360ce9f0" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_019ecc6e-8898-7614-9fdf-18e3c1e998b4" 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_019ecc6e-8898-71fb-a935-5a25b5c7d175" xlink:to="loc_dei_EntityTaxIdentificationNumber_019ecc6e-8898-7614-9fdf-18e3c1e998b4" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_019ecc6e-8898-7bdf-bd18-46708e7ccfb6" 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_019ecc6e-8898-71fb-a935-5a25b5c7d175" xlink:to="loc_dei_EntityAddressAddressLine1_019ecc6e-8898-7bdf-bd18-46708e7ccfb6" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine2_019ecc6e-8898-7e44-a41c-469af1422337" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityAddressAddressLine2"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ecc6e-8898-71fb-a935-5a25b5c7d175" xlink:to="loc_dei_EntityAddressAddressLine2_019ecc6e-8898-7e44-a41c-469af1422337" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_019ecc6e-8898-700d-bb7c-4beb168e863e" 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_019ecc6e-8898-71fb-a935-5a25b5c7d175" xlink:to="loc_dei_EntityAddressCityOrTown_019ecc6e-8898-700d-bb7c-4beb168e863e" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_019ecc6e-8898-7443-9b08-109a72115e06" 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_019ecc6e-8898-71fb-a935-5a25b5c7d175" xlink:to="loc_dei_EntityAddressStateOrProvince_019ecc6e-8898-7443-9b08-109a72115e06" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_019ecc6e-8898-7b3f-a515-65a9ddeab3cd" 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_019ecc6e-8898-71fb-a935-5a25b5c7d175" xlink:to="loc_dei_EntityAddressPostalZipCode_019ecc6e-8898-7b3f-a515-65a9ddeab3cd" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_019ecc6e-8898-77df-9bcc-81ba33f4c6eb" 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_019ecc6e-8898-71fb-a935-5a25b5c7d175" xlink:to="loc_dei_CityAreaCode_019ecc6e-8898-77df-9bcc-81ba33f4c6eb" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_019ecc6e-8898-7a78-8884-e1e98b4b4397" 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_019ecc6e-8898-71fb-a935-5a25b5c7d175" xlink:to="loc_dei_LocalPhoneNumber_019ecc6e-8898-7a78-8884-e1e98b4b4397" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_WrittenCommunications_019ecc6e-8898-7794-b1bb-6bbe22c47b5a" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_WrittenCommunications"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ecc6e-8898-71fb-a935-5a25b5c7d175" xlink:to="loc_dei_WrittenCommunications_019ecc6e-8898-7794-b1bb-6bbe22c47b5a" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SolicitingMaterial_019ecc6e-8898-7515-b558-f975ab800bd5" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_SolicitingMaterial"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ecc6e-8898-71fb-a935-5a25b5c7d175" xlink:to="loc_dei_SolicitingMaterial_019ecc6e-8898-7515-b558-f975ab800bd5" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_PreCommencementTenderOffer_019ecc6e-8898-7508-8b6c-91458f08bf87" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_PreCommencementTenderOffer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ecc6e-8898-71fb-a935-5a25b5c7d175" xlink:to="loc_dei_PreCommencementTenderOffer_019ecc6e-8898-7508-8b6c-91458f08bf87" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_PreCommencementIssuerTenderOffer_019ecc6e-8898-793e-81b9-804475010f23" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_PreCommencementIssuerTenderOffer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ecc6e-8898-71fb-a935-5a25b5c7d175" xlink:to="loc_dei_PreCommencementIssuerTenderOffer_019ecc6e-8898-793e-81b9-804475010f23" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_019ecc6e-8898-7006-9765-1dfd2859713d" 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_019ecc6e-8898-71fb-a935-5a25b5c7d175" xlink:to="loc_dei_Security12bTitle_019ecc6e-8898-7006-9765-1dfd2859713d" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_019ecc6e-8898-7cad-90ad-9df4ead5349e" 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_019ecc6e-8898-71fb-a935-5a25b5c7d175" xlink:to="loc_dei_TradingSymbol_019ecc6e-8898-7cad-90ad-9df4ead5349e" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_019ecc6e-8898-7c8e-a904-fb3094064fcc" 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_019ecc6e-8898-71fb-a935-5a25b5c7d175" xlink:to="loc_dei_SecurityExchangeName_019ecc6e-8898-7c8e-a904-fb3094064fcc" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_019ecc6e-8898-7ed5-9795-557db01d20ae" 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_019ecc6e-8898-71fb-a935-5a25b5c7d175" xlink:to="loc_dei_EntityEmergingGrowthCompany_019ecc6e-8898-7ed5-9795-557db01d20ae" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_019ecc6e-8898-7234-aa42-7fed2d67a95e" 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_019ecc6e-8898-71fb-a935-5a25b5c7d175" xlink:to="loc_dei_EntityCentralIndexKey_019ecc6e-8898-7234-aa42-7fed2d67a95e" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_019ecc6e-8898-7a42-9221-e5e11fab1988" 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_019ecc6e-8898-71fb-a935-5a25b5c7d175" xlink:to="loc_dei_AmendmentFlag_019ecc6e-8898-7a42-9221-e5e11fab1988" xlink:type="arc" order="22"/>
  </link:definitionLink>
</link:linkbase>
