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

    <schemaVersion>X0206</schemaVersion>

    <documentType>3/A</documentType>

    <periodOfReport>2014-08-18</periodOfReport>

    <dateOfOriginalSubmission>2014-08-21</dateOfOriginalSubmission>

    <noSecuritiesOwned>0</noSecuritiesOwned>

    <issuer>
        <issuerCik>0001588272</issuerCik>
        <issuerName>NexPoint Capital, Inc.</issuerName>
        <issuerTradingSymbol>N/A</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001617621</rptOwnerCik>
            <rptOwnerName>NexPoint Advisors, L.P.</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>300 CRESCENT COURT, SUITE 700</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>DALLAS</rptOwnerCity>
            <rptOwnerState>TX</rptOwnerState>
            <rptOwnerZipCode>75201</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>1</isOther>
            <officerTitle></officerTitle>
            <otherText>investment adviser</otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001615990</rptOwnerCik>
            <rptOwnerName>NexPoint Advisors GP, LLC</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>300 CRESCENT COURT, SUITE 700</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>DALLAS</rptOwnerCity>
            <rptOwnerState>TX</rptOwnerState>
            <rptOwnerZipCode>75201</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>0</isDirector>
            <isOfficer>0</isOfficer>
            <isTenPercentOwner>1</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle></officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeHolding>
            <securityTitle>
                <value>Common Stock, par value $0.001 per share</value>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>21739.13</value>
                    <footnoteId id="F1"/>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                    <footnoteId id="F2"/>
                </directOrIndirectOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <derivativeTable></derivativeTable>

    <footnotes>
        <footnote id="F1">This Amendment to the Initial Statement of Beneficial Ownership of Securities on Form 3, filed with the Securities and Exchange Commission on August 21, 2014, is being filed to correct the number of shares purchased by NexPoint Advisors, L.P.  The correct number of shares was disclosed in the prospectus supplement of the Issuer prior to any of the shares of the Issuer being sold to investors unaffilated with NexPoint Advisors, L.P.</footnote>
        <footnote id="F2">This Form 3 is being filed jointly by NexPoint Advisors, L.P. and NexPoint Advisors GP, LLC in connection with the effectiveness of the Issuer's Registration Statement on Form N-2 (File No. 333-196096).  NexPoint Advisors, L.P. directly owns 100% of the outstanding stock of the Issuer.  NexPoint Advisors GP, LLC, as the general partner of NexPoint Advisors, L.P., may be viewed as having investment power over all of the shares of the Issuer owned by NexPoint Advisors, L.P. NexPoint Advisors GP, LLC disclaims beneficial ownership of such shares except to the extent of its pecuniary interest therein.</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>/s/ Ethan K. Powell, President of NexPoint Advisors, L.P.</signatureName>
        <signatureDate>2015-04-29</signatureDate>
    </ownerSignature>

    <ownerSignature>
        <signatureName>/s/ James Dondero, Sole Member of NexPoint Advisors GP, LLC</signatureName>
        <signatureDate>2015-04-29</signatureDate>
    </ownerSignature>
</ownershipDocument>
