Arthur Thomas was an enlisted member of the Minnesota National Guard from 1953 through 1955. Enlisting in the Air Force in 1955, he served as a Russian language specialist at Wakkanai Air Station, Japan, until 1958. After attending St. Procopius Seminary in Lisle, Illinois, he was ordained in 1965 as a Roman Catholic priest for the diocese of New Ulm, Minnesota, where he served as a parish priest. In November 1968 he was commissioned as a U.S. Air Force Chaplain. From 1995 to 1997 he served as the 12th U.S. Air Force Chief of Chaplains and retired in 1997 as an Air Force Major General.