In 1939, Foulkes was serving as a major with the 3rd Brigade of the 1st Canadian Infantry Division. He went on to be a General Staff Officer with 3rd Canadian Infantry Division. After serving as a Brigade Commander from August 1942, he was appointed General Officer Commanding 2nd Canadian Infantry Division in January 1944 and led the division through the Normandy Campaign. In November 1944 he was made General Officer Commanding I Canadian Corps in Italy.