Bass has been married three times. He married his first wife, Carol Ann Owens, whom he met while doing research for the Army, in 1953. Owens died of colon cancer in 1993. His second marriage, in 1994, was to Annette Blackbourne, who died in 1997 from lung cancer. Later that year he married Carol Lee Hicks, who had been a friend of his since childhood. Bass has three sons, Charlie, William Marvin IV, and Jim. Bass is an atheist.