Private First Class Mercer was a member of Company C, 1st Battalion, 7th Marines, 1st Marine Division. He was Killed in Action while patrolling northeast of the "Punchbowl" preparing to attack "Heartbreak Ridge" in North Korea on 6 November 1951.

Mercer was awarded the Purple Heart, the Combat Action Ribbon, the Korean Service Medal, the United Nations Service Medal, the National Defense Service Medal, the Korean Presidential Unit Citation and the Republic of Korea War Service Medal.