Among his notable roles are in the films Prisoner of War, The Longest Day, North Dallas Forty, and Mommie Dearest. Television roles have included the British crime series The Baron (1965-1966), S.W.A.T., Hollywood Wives and Dallas, in which he played an impostor pretending to be Jock Ewing. Gunsmoke fans will remember Forrest as perhaps the only man to ever gun down Matt Dillon in the episode Mannon. Dillon survived to later shoot Mannon.
Forrest has been married to Christine Carilas since 1949; they have three sons.