<?xml version="1.0"?>
<ownershipDocument>

    <schemaVersion>X0306</schemaVersion>

    <documentType>5</documentType>

    <periodOfReport>2021-12-31</periodOfReport>

    <notSubjectToSection16>0</notSubjectToSection16>

    <form3HoldingsReported>0</form3HoldingsReported>

    <form4TransactionsReported>0</form4TransactionsReported>

    <issuer>
        <issuerCik>0001418076</issuerCik>
        <issuerName>SLR Investment Corp.</issuerName>
        <issuerTradingSymbol>SLRC</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001240586</rptOwnerCik>
            <rptOwnerName>SPOHLER BRUCE J</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>C/O SLR INVESTMENT CORP.</rptOwnerStreet1>
            <rptOwnerStreet2>500 PARK AVENUE</rptOwnerStreet2>
            <rptOwnerCity>NEW YORK</rptOwnerCity>
            <rptOwnerState>NY</rptOwnerState>
            <rptOwnerZipCode>10022</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Co-Chief Executive Officer</officerTitle>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeTransaction>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionDate>
                <value>2021-12-04</value>
            </transactionDate>
            <deemedExecutionDate></deemedExecutionDate>
            <transactionCoding>
                <transactionFormType>5</transactionFormType>
                <transactionCode>G</transactionCode>
                <equitySwapInvolved>0</equitySwapInvolved>
            </transactionCoding>
            <transactionTimeliness>
                <value></value>
            </transactionTimeliness>
            <transactionAmounts>
                <transactionShares>
                    <value>121506</value>
                    <footnoteId id="F1"/>
                </transactionShares>
                <transactionPricePerShare>
                    <value>0.00</value>
                </transactionPricePerShare>
                <transactionAcquiredDisposedCode>
                    <value>A</value>
                </transactionAcquiredDisposedCode>
            </transactionAmounts>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>2371524</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>I</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value>See Footnotes</value>
                    <footnoteId id="F2"/>
                    <footnoteId id="F3"/>
                    <footnoteId id="F4"/>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeTransaction>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock</value>
            </securityTitle>
            <transactionCoding>
                <transactionFormType></transactionFormType>
            </transactionCoding>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>67256</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">Pursuant to an inheritance, Bruce J. Spohler became co-trustee of a trust in which he and certain members of his immediate family are beneficiaries (the &quot;Spohler Trust&quot;).  Mr. Spohler disclaims beneficial ownership, except to the extent of his pecuniary interest.</footnote>
        <footnote id="F2">The total includes 121,506 shares held by the Spohler Trust (which are reported as having been received on this Form 5), 250,005 shares of the Issuer held by Solar Capital Partners Employee Stock Plan, LLC (the &quot;SCP Plan&quot;). The SCP Plan is controlled by SLR Capital Partners LLC (f/k/a Solar Capital Partners, LLC) (&quot;SLR Capital Partners&quot;). Bruce J. Spohler and Michael S. Gross may be deemed to indirectly beneficially own a portion of the shares held by the SCP Plan by virtue of their collective ownership interest in SLR Capital Partners.</footnote>
        <footnote id="F3">(Continued from Footnote (2)) In addition, the total includes 1,285,013 shares of the Issuer held by Solar Capital Investors, LLC (&quot;Solar Capital I&quot;) and 715,000 shares of the Issuer held by Solar Capital Investors II, LLC (&quot;Solar Capital II&quot;), a portion of both of which may be deemed to be indirectly beneficially owned by Mr. Spohler, Mr. Gross and a grantor retained annuity trust setup by and for Mr. Gross by virtue of their collective ownership interest therein.</footnote>
        <footnote id="F4">Mr. Spohler disclaims beneficial ownership of any of the Issuer's securities directly held by the SCP Plan, Solar Capital I, Solar Capital II and the Spohler Trust, except to the extent of his pecuniary interest therein, and this report shall not be deemed an admission that Mr. Spohler is the beneficial owner of such securities for purposes of Section 16 or any other purpose.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>BRUCE J. SPOHLER, /s/ Bruce J. Spohler, Name: Bruce J. Spohler</signatureName>
        <signatureDate>2022-02-14</signatureDate>
    </ownerSignature>
</ownershipDocument>
