In a career that has spanned nearly 50 years, Whitman, who had been an amateur boxer, has appeared in more than 75 feature films, making his debut in a bit role in "When Worlds Collide" (1951). He continued in relatively small roles like a football player in "The All-American" and a sergeant in "The Veils of Baghdad" (both 1953) and a bandit in "Passion" (1954). Whitman finally began to get some real notice as one of "Darby's Rangers" (1958), and subsequently played the circus roustabout cad who woos Joanne Woodward in "The Sound and the Fury" (1959) and Boaz, second husband to the biblical Ruth and ancestor of King David in "The Story of Ruth" (1960). He had good opportunities in "The Comancheros" and "Francis of Assisi" (both 1961) before his breakthrough role as Jim Fuller in "The Mark". Cast against type as a sexually-confused man with a domineering mother and an ineffectual father who is attracted to young girls, he delivered an excellent, nuanced performance. (This study of "deviance" was also a breakthrough for Hollywood and showed the decline of the Breen Office and Motion Picture Code, which would be replaced by the ratings system in five years.)

Despite his Oscar nomination, Whitman remained typecast in roles that played off his machismo, like the army lieutenant in the all-star "The Longest Day" (1962). Exceptions included "Shock Treatment" (1964), in which he was an out-of-work actor who goes undercover at a mental institution, and "Those Magnificent Men in Their Flying Machines" (1965), as the hero of a ribald intrigue. "Sands of the Kalahari" (1965) had Whitman leading air crash survivors through monkey-mad terrain, but was well received. but not so "An American Dream" (1966), based on the Norman Mailer novel about a murderous TV commentator. Turning to the small screen, Whitman co-produced and starred in "Cimarron Strip" (CBS, 1967-71). When he attempted to return to features after the series, he found a changed Hollywood and found himself taking leads and second leads in low-budget independent fare. He was the bigamist sheriff picked up by the ladies of "Crazy Mama" (1975), a New World production which has since become rediscovered because it was one of Jonathan Demme's early directorial efforts. "Eaten Alive" (1976), however, was a silly yarn about a psychopath with a crocodile on his front lawn directed by Tobe Hooper. He got a chance to play a real-life hero, oil well fire fighter Red Adair in "Oil" (1976) but by 1980 was reduced to playing Rev. Jim Johnson in "Guyana: Cult of the Damned", an exploitative and lackluster fictional dramatization of the Jonestown massacre. Whitman's films in the 80s and 90s had titles such as "Demonoid" (1981), and "Vultures in Paradise" (1984). By the 90s, he was playing decidedly supporting roles such as in "Trial By Jury" (1994).

The small screen, however, offered meatier roles. In the 50s, he appeared in 26 episodes of the syndicated series "Highway Patrol" playing sidekick to Broderick Crawford, and also appeared in episodes of network series. Whitman made his TV movie debut in 1970 playing a heart surgeon who uncovers sinister forces at a research foundation in "The Man Who Wanted to Live Forever" (ABC). He starred in an Irwin Allen would-be pilot, playing a "Voyage to the Bottom of the Sea"-type admiral in "City Beneath the Sea" (NBC, 1971) and co-starred in the miniseries "Harold Robbins' 'The Pirate'" (CBS, 1978). He was also active in guest spots in the 70s and 80s, making several appearances on "Murder, She Wrote" (CBS). In 1990, he had a recurring role on "Knots Landing" (CBS) creating tension in the life of Paige Matheson, and he has continued to appear in TV-movies, more recently as a stroke victim still trying to run a ranch in "Wounded Heart" (USA Network, 1995). Closer to the fans of Whitman's rough-'n'-tumble era of filmmaking, he has made several guest appearances, beginning in 1994, on "Walker, Texas Ranger" (CBS) playing an old pal of Chuck Norris.