In the 1930s, Kerr served as Parliamentary Private Secretary to Alfred Duff Cooper, starting in 1933 when Cooper was Financial Secretary to the War Office. During the Second World War, he served in a balloon squadron in the Royal Air Force and briefly held office as Parliamentary Secretary to the Ministry of Health in the 1945 caretaker government.
From the 1930s to the 1940s, Kerr held various roles for Alfred Duff Cooper, including Parliamentary Assistant and later, a member of the Ministry of Health. He also served in the Royal Air Force during World War II.