SgtMaj Gene Overstreet entered the Marine Corps in June 1966 and completed recruit training at Marine Corps Recruit Depot, San Diego, CA, followed by Basic Infantry Training School at Camp Pendleton, CA. Upon completion of school, he was assigned to the 1st Military Police Battalion, 3rd Marine Division, Republic of Vietnam. Once he returned to the states, he was reassigned to the Infantry Training Regiment at Camp Pendleton. His promotion to First Sergeant in February 1979 led to his second assignment on Okinawa as the First Sergeant, Headquarters and Service Co., 8th Engineer Battalion. He became the Inspector Sergeant Major, MCAGCC, Twentynine Palms. Returning to Marine Corps Recruit Depot, San Diego, he served as a Battalion and Regimental Sergeant Major in the Recruit Training Regiment. He was then transferred to Camp Lejeune, NC, where he served as the 6th Marines Sergeant Major, followed by duty as Regimental Sergeant Major, 12th Marines, Okinawa.

On April 6, 1990, SgtMaj Overstreet was posted as Depot Sergeant Major at San Diego. He was selected as the 12th Sergeant Major of the Marine Corps in April 1991, and assumed the post on June 28, 1991. His personal decorations include: Distinguished Service Medal, Superior Service Medal, Meritorious Service Medal, Navy Commendation Medal, Navy Achievement Medal, and Combat Action Ribbon.