Private Mahar was a member of Company C, 1st Battalion, 34th Infantry Regiment, 24th Infantry Division. He was wounded in action fighting the enemy in South Korea of 8 August 1950 and died later that day.

Mahar was awarded the Purple Heart, the Good Conduct Medal, the Combat Infantryman's Badge, 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.