6-K

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

Form 6-K

REPORT OF FOREIGN PRIVATE ISSUER

PURSUANT TO RULE 13a-16 OR 15d-16

UNDER THE SECURITIES EXCHANGE ACT OF 1934

For the month of October 2021

Commission File Number 001-35866

KNOT OffshorePartners LP

(Translation of registrant’s name intoEnglish)

2 Queen’s Cross,

Aberdeen, Aberdeenshire

AB15 4YB

United Kingdom

(Address of principal executive office)

Indicate by check mark whether the registrant files or will file annual reports under cover of Form 20-F or Form 40-F.

Form 20-F   x             Form 40-F   ¨

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101 (b)(1).

Yes   ¨             No  x

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101 (b)(7).

Yes   ¨             No  x

On October 1, 2021, KNOT Offshore Partners LP (the “Partnership”) held its previously-adjourned 2021 annual meeting of limited partners (the “2021 Annual Meeting”) at 3:00 P.M. (UK time) at One Elmfield Park, Bromley, BR1 1LU, United Kingdom. At the 2021 Annual Meeting, a resolution was passed to re-elect Hans Petter Aas as a Class IV Director of the Partnership whose term will expire at the 2025 annual meeting of limited partners.

THIS REPORT ON FORM 6-K IS HEREBY INCORPORATED BY REFERENCE INTO THE REGISTRATION STATEMENT ON FORM F-3 (NO. 333-248518) OF THE REGISTRANT.

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SIGNATURE

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

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