Mixon was commissioned as a second lieutenant of Infantry in 1975 and was subsequently assigned to the 2nd Battalion of the 505th Parachute Regiment, 82nd Airborne Division.

While there, he served on the division staff and commanded Company B of the 1st Battalion of the 15th Infantry Regiment in Kitzingen, Germany.

From 1988 to 1991, Mixon served as the executive officer of the 3rd Battalion of the 502nd Infantry Regiment, and chief of plans for the 101st Airborne Division at Fort Campbell.

Mixon was then promoted to chief of staff, XVIII Airborne Corps in Fort Bragg from July 2002 until June 2003.

During that time he deployed to Baghram Air Base in Afghanistan, where he participated in Operation Enduring Freedom as the director of the staff of the Combined Joint Task Force 180.

On March 31, 2010, Army Secretary John McHugh said, “We consider the matter closed as of today,” and went on to say that Mixon would "not be reprimanded or asked to resign" because of the comments.