Robinson began his acting career in summer stock theatre and repertory companies, and eventually made his way to the Broadway stage, where he appeared in Shakespeare's As You Like It and Much Ado About Nothing, as well as several other plays by the age of 19. His first film role was as the notorious Emperor Caligula in The Robe (1953), which he reprised in Demetrius and the Gladiators (1954).

This was followed by roles in a variety of films, including The Virgin Queen (1955) starring Bette Davis, My Man Godfrey (1957) with David Niven and June Allyson, Woody Allen's comedy Everything You Always Wanted to Know About Sex* (*But Were Afraid to Ask) (1972), and Bram Stoker's Dracula (1992). He was also featured on two Folkways albums of Shakespeare: Othello: william Shakespeare and William Shakespeare: King Richard III, which were both released in 1964.

His new-found Celebrity after appearing in The Robe and its sequel Demetrius and the Gladiators reportedly went to his head, and he became extremely difficult to work with. In addition the volatile actor began experimenting recklessly with drugs. He was arrested and booked in 1958 for possession of narcotics (methadone) and after a trial sentenced to a year in jail; his conviction was overturned on appeal, however. While free on bail, the incident and resulting bad press ruined his acting career.

Robinson was married twice: to Pauline Flowers from 1960 until her death in 2002 and to Gloria Casas from 2004 until his death. He had one son with Flowers.

Of his many television guest spots, they included Star Trek: The Original Series ("Elaan of Troyius"), the soap opera Days of Our Lives (Monty, the homeless drunk), The Wild Wild West (Dr. Maitland in "The Night of the Sedgewick Curse"), Planet of the Apes and the title role in Sid & Marty Krofft's Dr. Shrinker, prominently featured on The Krofft Supershow. He also guest-starred as Cassius Thorne in the Buck Rogers in the 25th Century episode "Planet of the Amazon Women". He appeared in two episodes of the situation comedy Bewitched as Julius Caesar (1969) and as Tabitha's tutor, Professor Poindexter Phipps (1970) and on an episode of Tales of the Gold Monkey as the Governor in "Last Chance Louie". Robinson also had a cameo in an episode of Barney Miller, "The Sniper."

After scraping up work outside the entertainment industry as a cook and landlord, he recovered from his drug addiction and eventually married. Resuming work in obscure bit parts, he had another career relapse when he was forced to spend 15 months in jail after all for an old warrant served on him for unknowingly missing a court date during his earlier retrial. Robinson credited letters of encouragement from friend Bette Davis with helping him find the strength to overcome his problems. She helped him get his first film role in 13 years, in 1971's Bunny O'Hare.

For the cinema he played the role of Monroe Feather in the blaxploitation movie Three the Hard Way (1974) starring Jim Brown, Jim Kelly and Fred Williamson. The character Feather was recreated in the movie Undercover Brother. He also appeared in Born Again (1978), the film adaptation of the book of the same title, about Watergate figure, Charles W. Colson. Robinson played Colson's attorney and Dean Jones starred as Colson. During 1974, he played the museum Director in a 1975 episode of the ABC supernatural show Kolchak: The Night Stalker entitled "Chopper" and a dual role in a Banacek mystery called "Now You See Him, Now You Don't." In 1977, he appeared in the final episode of the NBC situation comedy The Kallikaks.

Before retiring, Robinson was the host and narrator for the Discovery Channel special (and later documentary series) Beyond Bizarre from 1997 to 2000.