Upon the outbreak of the Korean War, McHugh took part in combat operations with the 1st Marine Brigade and, subsequently, the 1st Marine Division as first sergeant, Company H, 3rd Battalion 5th Marines during the Battle of Pusan Perimeter, Battle of Inchon, Battle of Seoul, and Battle of Chosin Reservoir campaigns. He was promoted to master sergeant in Korea in December 1950, and returned to the United States in March 1951.