Armstrong played on the PGA Tour from 1974 to 1984. His best finishes were a trio of second places: a tie for second at the 1974 Sahara Invitational, second at the 1975 Pensacola Open, and a second-place tie at the 1977 Western Open. His best finish in a major was a fifth-place tie at the 1978 Masters Tournament. His 280 total in 1978 was a record low for a first-time Masters participant.