Private Leonello was a member of Company A, 1st Battalion, 7th Cavalry Regiment, 1st Cavalry Division. He was Killed in Action while fighting the enemy in North Korea on 24 September 1951.

Leonello was awarded the Purple Heart, 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.