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) November 1, 2018

ALLISON TRANSMISSION HOLDINGS, INC.

(Exact name of registrant as specified in its charter)

Registrant’s telephone number, including area code (317) 242-5000

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):

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter).

Emerging growth company  ☐

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act.  ☐

On November 1, 2018, the Board of Directors (“Board”) of Allison Transmission Holdings, Inc. (the “Company”), upon the recommendation of the Nominating and Corporate Governance Committee, appointed Carolann Haznedar to serve as a member of the Company’s Board, effective immediately, with a term to expire at the Company’s 2019 annual meeting of stockholders. The appointment of Ms. Haznedar increases the size of the Board to ten members. In addition, Ms. Haznedar has been appointed to serve on the Audit Committee of the Board.

As a non-management director, Ms. Haznedar will receive compensation in accordance with the Company’s Third Amended and Restated Non-Employee Director Compensation Policy (“Policy”). (See the Policy filed as Exhibit 10.25 to the Company’s Annual Report on Form 10-K for the year ended December 31, 2017 with the Securities and Exchange Commission (“SEC”) on February 15, 2018.) In addition, it is expected that Ms. Haznedar will execute the Company’s standard form of director indemnification agreement. (See the Form of Director Indemnification Agreement filed as Exhibit 10.9 to Amendment No. 2 to the Company’s Registration Statement on Form S-1 filed with the SEC on May 16, 2011.) There was no arrangement or understanding pursuant to which Ms. Haznedar was elected as a director, and there are no related party transactions between the Company and Ms. Haznedar

A copy of the Company’s press release announcing the appointment of Ms. Haznedar to the Board is attached hereto as Exhibit 99.1 and the information set forth therein is incorporated herein by reference.

(d) Exhibits.

SIGNATURES

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 99.1

ALLISON TRANSMISSION ADDS CAROLANN HAZNEDAR TO BOARD OF DIRECTORS

INDIANAPOLIS — November 1, 2018 — Allison Transmission Holdings Inc. (NYSE: ALSN), the largest global provider of commercial duty fully-automatic transmissions, announced today that Carolann I. Haznedar has been appointed to its Board of Directors, effective immediately. The appointment of Ms. Haznedar increases the size of the Board to ten members.

Ms. Haznedar is the recently retired Senior Vice President Americas for DuPont Performance Materials, a global business serving the automotive and industrial industries. Ms. Haznedar has more than 30 years of management experience, leading several global businesses in different industries during her tenure at DuPont.

“We are pleased to welcome Carolann as a new independent member of our Board of Directors,” said Lawrence E. Dewey, Chairman of the Board of Directors. “We are focused in constantly strengthening the composition of our Board as we continue to seek excellence in line with our standing as a premier industrial company. Carolann’s strong operational experience and clear business leadership is an important and invaluable asset to our Board.”

Ms. Haznedar’s term will expire at the 2019 annual meeting of stockholders. In addition, Ms. Haznedar will also serve as a member of the Board’s Audit Committee.

Carolann Haznedar

Carolann Haznedar held various positions with E.I. du Pont de Nemours and Company from 1981 until her retirement in June 2016. Most recently, she served as Senior Vice President, Americas for DuPont Performance Materials from September 2015 until June 2016, Senior Vice President, Americas, Packaging & Industrial Polymers from October 2011 until September 2015, and Senior Vice President, Global Packaging & Industrial Polymers from July 2008 until October 2011. Prior to E. I. du Pont de Nemours and Company, Ms. Haznedar worked for EDO Aire Corporation. Ms. Haznedar serves as a member of the Board of Directors of Harsco Corporation.

About Allison Transmission

Allison Transmission (NYSE: ALSN) is the world’s largest manufacturer of fully automatic transmissions for medium- and heavy-duty commercial vehicles and is a leader in electric hybrid-propulsion systems for city buses. Allison transmissions are used in a variety of applications including refuse, construction, fire, distribution, bus, motorhomes, defense and energy. Founded in 1915, the company is headquartered in Indianapolis, Indiana, USA and employs approximately 2,700 people worldwide. With a market presence in more than 80 countries, Allison has regional headquarters in the Netherlands, China and Brazil with manufacturing facilities in the U.S., Hungary and India. Allison also has approximately 1,400 independent distributor and dealer locations worldwide. For more information, visit allisontransmission.com.

Contacts

Investor Relations

ir@allisontransmission.com

(317) 242-3078

Media Relations

media@allisontransmission.com

(317) 242-5000