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

    <schemaVersion>X0202</schemaVersion>

    <documentType>3</documentType>

    <periodOfReport>2005-11-08</periodOfReport>

    <noSecuritiesOwned>0</noSecuritiesOwned>

    <issuer>
        <issuerCik>0001336047</issuerCik>
        <issuerName>Boardwalk Pipeline Partners, LP</issuerName>
        <issuerTradingSymbol>BWP</issuerTradingSymbol>
    </issuer>

    <reportingOwner>
        <reportingOwnerId>
            <rptOwnerCik>0001343049</rptOwnerCik>
            <rptOwnerName>Gafvert Rolf A</rptOwnerName>
        </reportingOwnerId>
        <reportingOwnerAddress>
            <rptOwnerStreet1>3800 FREDERICA STREET</rptOwnerStreet1>
            <rptOwnerStreet2></rptOwnerStreet2>
            <rptOwnerCity>OWENSBORO</rptOwnerCity>
            <rptOwnerState>KY</rptOwnerState>
            <rptOwnerZipCode>42301</rptOwnerZipCode>
            <rptOwnerStateDescription></rptOwnerStateDescription>
        </reportingOwnerAddress>
        <reportingOwnerRelationship>
            <isDirector>1</isDirector>
            <isOfficer>1</isOfficer>
            <isTenPercentOwner>0</isTenPercentOwner>
            <isOther>0</isOther>
            <officerTitle>Co-President</officerTitle>
            <otherText></otherText>
        </reportingOwnerRelationship>
    </reportingOwner>

    <nonDerivativeTable>
        <nonDerivativeHolding>
            <securityTitle>
                <value>No securities beneficially owned</value>
                <footnoteId id="F1"/>
            </securityTitle>
            <postTransactionAmounts>
                <sharesOwnedFollowingTransaction>
                    <value>0</value>
                </sharesOwnedFollowingTransaction>
            </postTransactionAmounts>
            <ownershipNature>
                <directOrIndirectOwnership>
                    <value>D</value>
                </directOrIndirectOwnership>
                <natureOfOwnership>
                    <value></value>
                </natureOfOwnership>
            </ownershipNature>
        </nonDerivativeHolding>
    </nonDerivativeTable>

    <footnotes>
        <footnote id="F1">This Form 3 is being filed in connection with the effectiveness of the Issuer?s Registration Statement on Form S-1 which was filed on August 16, 2005 (File No. 333-127578).</footnote>
    </footnotes>

    <remarks></remarks>

    <ownerSignature>
        <signatureName>Kenneth J. Zinghini, attorney in fact</signatureName>
        <signatureDate>2005-11-08</signatureDate>
    </ownerSignature>
</ownershipDocument>
