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): January 26, 2016

FIRSTMERIT CORPORATION

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code: (330) 996-6300

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:

On January 26, 2016, FirstMerit Corporation (the “Corporation”) announced earnings for the quarter ended December 31, 2015. A copy of the press release and certain financial information for this period is attached as Exhibit 99.1 hereto and incorporated by reference herein. A supplemental information package to such press release is attached as Exhibit 99.2 hereto and incorporated by reference herein.

Pursuant to General Instruction B.2 of Form 8-K, the information in this Item 2.02 is being furnished to the Securities and Exchange Commission and shall not be deemed to be “filed” for purposes of Section 18 of the Securities Exchange Act of 1934 or otherwise subject to the liabilities of that section. Furthermore, the information in this Item 2.02 shall not be deemed to be incorporated by reference into the filings of the Corporation under the Securities Act of 1933.

On January 26, 2016, the Corporation and Huntington Bancshares Incorporated (“Huntington”) issued a joint press release announcing the signing of a definitive merger agreement pursuant to which, on the terms and subject to the conditions set forth therein, (i) a newly formed wholly owned subsidiary of Huntington will merge with and into the Corporation (the “Merger”), (ii) as soon as reasonably practicable following the Merger, the Corporation will merge with and into Huntington (the “Second Step Merger”) and (iii) following the Second Step Merger, FirstMerit Bank, National Association will merge with and into The Huntington National Bank. A copy of the joint press release announcing the transaction is attached hereto as Exhibit 99.3.

(d) Exhibits.

Caution regarding Forward-Looking Statements

This communication may contain certain forward-looking statements, including certain plans, expectations, goals, projections, and statements about the benefits of the proposed transaction, the merger parties’ plans, objectives, expectations and intentions, the expected timing of completion of the transaction, and other statements that are not historical facts. Such statements are subject to numerous assumptions, risks, and uncertainties. Statements that do not describe historical or current facts, including statements about beliefs and expectations, are forward-looking statements. Forward-looking statements may be identified by words such as expect,

anticipate, believe, intend, estimate, plan, target, goal, or similar expressions, or future or conditional verbs such as will, may, might, should, would, could, or similar variations. The forward-looking statements are intended to be subject to the safe harbor provided by Section 27A of the Securities Act of 1933, Section 21E of the Securities Exchange Act of 1934, and the Private Securities Litigation Reform Act of 1995.

While there is no assurance that any list of risks and uncertainties or risk factors is complete, below are certain factors which could cause actual results to differ materially from those contained or implied in the forward-looking statements: changes in general economic, political, or industry conditions, uncertainty in U.S. fiscal and monetary policy, including the interest rate policies of the Federal Reserve Board, volatility and disruptions in global capital and credit markets; movements in interest rates; competitive pressures on product pricing and services; success, impact, and timing of Huntington’s and FirstMerit’s respective business strategies, including market acceptance of any new products or services implementing Huntington’s “Fair Play” banking philosophy; the nature, extent, timing, and results of governmental actions, examinations, reviews, reforms, regulations, and interpretations, including those related to the Dodd-Frank Wall Street Reform and Consumer Protection Act and the Basel III regulatory capital reforms, as well as those involving the OCC, Federal Reserve, FDIC, and CFPB, and the regulatory approval process associated with the merger; the possibility that the proposed transaction does not close when expected or at all because required regulatory, shareholder or other approvals are not received or other conditions to the closing are not satisfied on a timely basis or at all; the possibility that the anticipated benefits of the transaction are not realized when expected or at all, including as a result of the impact of, or problems arising from, the integration of the two companies or as a result of the strength of the economy and competitive factors in the areas where Huntington and FirstMerit do business; the possibility that the transaction may be more expensive to complete than anticipated, including as a result of unexpected factors or events; diversion of management’s attention from ongoing business operations and opportunities; potential adverse reactions or changes to business or employee relationships, including those resulting from the announcement or completion of the transaction; Huntington’s ability to complete the acquisition and integration of FirstMerit successfully; and other factors that may affect future results of Huntington and FirstMerit. Additional factors that could cause results to differ materially from those described above can be found in Huntington’s Annual Report on Form 10-K for the year ended December 31, 2014 and in its subsequent Quarterly Reports on Form 10-Q, including for the quarter ended September 30, 2015, each of which is on file with the Securities and Exchange Commission (the “SEC”) and available in the “Investor Relations” section of Huntington’s website, http://www.huntington.com, under the heading “Publications and Filings” and in other documents Huntington files with the SEC, and in FirstMerit’s Annual Report on Form 10-K for the year ended December 31, 2014 and in its subsequent Quarterly Reports on Form 10-Q, including for the quarter ended September 30, 2015, each of which is on file with the SEC and available in the “Investors” section of FirstMerit’s website, http://www.firstmerit.com, under the heading “Publications & Filings” and in other documents FirstMerit files with the SEC.

All forward-looking statements speak only as of the date they are made and are based on information available at that time. Neither Huntington nor FirstMerit assumes any obligation to update forward-looking statements to reflect circumstances or events that occur after the date the forward-looking statements were made or to reflect the occurrence of unanticipated events except as required by federal securities laws. As forward-looking statements involve significant risks and uncertainties, caution should be exercised against placing undue reliance on such statements.

Important Additional Information

In connection with the proposed transaction, Huntington will file with the SEC a Registration Statement on Form S-4 that will include a Joint Proxy Statement of Huntington and FirstMerit and a Prospectus of Huntington, as well as other relevant documents concerning the proposed transaction. The proposed transaction involving Huntington and FirstMerit will be submitted to FirstMerit’s stockholders and Huntington’s stockholders for their consideration. This communication does not constitute an offer to sell or the solicitation of an offer to buy any securities or a solicitation of any vote or approval. STOCKHOLDERS OF HUNTINGTON AND STOCKHOLDERS OF FIRSTMERIT ARE URGED TO READ THE REGISTRATION STATEMENT AND THE JOINT PROXY STATEMENT/PROSPECTUS REGARDING THE TRANSACTION WHEN IT BECOMES AVAILABLE AND ANY OTHER RELEVANT DOCUMENTS FILED WITH THE SEC, AS WELL AS ANY AMENDMENTS OR SUPPLEMENTS TO THOSE DOCUMENTS, BECAUSE THEY WILL CONTAIN IMPORTANT INFORMATION. Stockholders will be able to obtain a free copy of the definitive joint proxy statement/prospectus, as well as other filings containing information about Huntington and FirstMerit, without charge, at the SEC’s website (http://www.sec.gov). Copies of the joint proxy statement/prospectus and the filings with the SEC that will be incorporated by reference in the joint proxy statement/prospectus can also be obtained, without charge, by directing a request to Huntington Investor Relations, Huntington Bancshares Incorporated, Huntington Center, HC0935, 41 South High Street, Columbus, Ohio 43287, (800) 576-5007 or to FirstMerit Corporation, Attention: Thomas P. O’Malley, III Cascade Plaza, Akron, Ohio 44308, (330) 384-7109.

Participants in the Solicitation

Huntington, FirstMerit, and certain of their respective directors, executive officers and employees may be deemed to be participants in the solicitation of proxies in respect of the proposed transaction. Information regarding Huntington’s directors and executive officers is available in its definitive proxy statement, which was filed with the SEC on March 12, 2015, and certain of its Current Reports on Form 8-K. Information regarding FirstMerit’s directors and executive officers is available in its definitive proxy statement, which was filed with the SEC on March 6, 2015, and certain of its Current Reports on Form 8-K. Other information regarding the participants in the proxy solicitation and a description of their direct and indirect interests, by security holdings or otherwise, will be contained in the joint proxy statement/prospectus and other relevant materials filed with the SEC. Free copies of this document may be obtained as described in the preceding paragraph.

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 hereunto duly authorized.

EXHIBIT INDEX