Roberts played the role of "Rooster" in the 1970s television series Baretta.
Roberts starred in the short-lived 1983 television series Manimal, appearing in five of the eight episodes which aired, as Tyrone C. Earl.
In 1988, Roberts played the role of Vern in the hit film Rain Man.
His other appearances include Bosom Buddies, Quantum Leap, The Incredible Hulk, Double Trouble, Friends, MacGyver, and Seinfeld.
On September 18, 1976, Roberts married actress Pamela Frey, whom he met in an acting class taught by Lillian Randolph.