O'Shea was awarded the Medal of Honor for action near Le Catelet, France, 29 September 1918. His citation reads, "Becoming separated from their platoon by a smoke barrage, Cpl. O'Shea, with 2 other soldiers, took cover in a shell hole well within the enemy's lines. Upon hearing a call for help from an American tank, which had become disabled 30 yards from them, the 3 soldiers left their shelter and started toward the tank under heavy fire from German machineguns and trench mortars. In crossing the fire-swept area Cpl. O'Shea was mortally wounded and died of his wounds shortly afterwards."