Sergeant First Class McMillian was a medic with the Medical Company, 38th Infantry Regiment, 2nd Infantry Division. He was listed as Missing in Action while tending his wounded comrades in South Korea on 12 February 1951. He was presumed dead on 19 February 1954. His remains were not recovered. His name is inscribed on the Courts of the Missing at the Honolulu Memorial.

McMillian was awarded the Purple Heart, the Combat Medical 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.