UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d) of the

Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): July 16, 2012

Northern Tier Energy LLC

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code: (203) 244-6550

Not Applicable.

(Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions (see General Instruction A.2. below):

On July 16, 2012, Northern Tier Energy LP (the “Partnership”), an affiliate of Northern Tier Energy LLC, commenced an initial public offering (the “Offering”) of 16,250,000 common units representing limited partner interests in the Partnership (the “Common Units”) pursuant to a registration statement filed with the Securities and Exchange Commission (the “Commission”). The Partnership will grant the underwriters a 30-day option to purchase up to an additional 2,437,500 Common Units. The Common Units will be listed on the New York Stock Exchange and trade under the symbol “NTI.”

A registration statement relating to these securities has been filed with the Commission but has not yet become effective. These securities may not be sold nor may offers to buy be accepted prior to the time the registration statement becomes effective. The registration statement is available on the SEC’s web site at http://www.sec.gov under the Partnership’s name, Northern Tier Energy LP. This Form 8-K shall not constitute an offer to sell or a solicitation of an offer to buy, nor shall there be any sale of these securities in any state or jurisdiction in which such an offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such state or jurisdiction.

In accordance with General Instruction B.2 of Form 8-K, the information set forth in this Item 7.01 shall not be deemed to be “filed” for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), or otherwise subject to the liabilities of that section, nor shall such information be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended, or the Exchange Act, except as shall be expressly set forth by specific reference in such a filing.

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.