Nelson entered the military service in 1942 as a second lieutenant in the United States Army Air Corps during World War II. He served in the armed forces until discharge in 1946 as a lieutenant colonel with two years of service in the European Theater of Operations. He remained a member of the National Guard and Reserves after leaving the military. He was a member of the State board of bar examiners from 1946 to 1948. He was also mayor of Augusta in 1947 and 1948.