Benson was born Robin David Segal in Dallas to Jewish parents, Gerald Charles Segal and Freda Ann Benson. His sister is Shelli Segal, designer for the clothing line known as Laundry by Shelli Segal.
Benson made his Broadway debut in The Rothschilds. Benson had an early role on the daytime soap Search for Tomorrow (1971–72). As a film star, Benson was popular for roles of teens in coming-of-age films, such as in 1972's Jory (his screen debut), and as Billy Joe McAllister in Ode to Billy Joe (1976).
He was listed as one of twelve "Promising New Actors of 1976" in John Willis' Screen World, Vol 28. , and auditioned for the role of Luke Skywalker in Star Wars (1977), but lost the role to Mark Hamill. He received critical acclaim for his role as the hockey play, Nick Peterson, in Ice Castles (1978).
Other notable performances include Death Be Not Proud and Lucky Lady, both in 1975, and One on One co-starring Annette O'Toole in 1977. Also in 1977 came the TV movie The Death of Richie, co-starring actor Ben Gazzara. He played the romantic lead in 1978's Ice Castles. In 1981, he costarred with Rod Steiger in the film The Chosen, based on the Chaim Potok book of the same name. Also in the early 1980's, he appeared as a young man with a learning disability in the made-for-television film Two of a Kind, along with George Burns playing the role of his "Grand-Poppy". In 1984 he costarred among others with Paul Newman in "Harry and Son". In Disney's animated feature film Beauty and the Beast, Benson demonstrated his vocal abilities by providing the voice of Beast. Some critics claim he did such a good job the voice was nearly unrecognizable as Benson's. He would later reprise the role in the Kingdom Hearts role-playing game series. This role led to other voice work for animated features, including the widely popular Prince Valiant cartoon series, as well as the heroic Able Squad leader J.T. Marsh on Exosquad. Benson also lends his voice to some computer and video game work, such as the voice of Prince Alexander in the computer game King's Quest VI: Heir Today, Gone Tomorrow.
Benson directed over 100 sitcom episodes including Friends, Sabrina, an entire season of Ellen, and two seasons of Thunder Alley.
Benson is currently a visiting professor at New York University's Tisch School of the Arts, having previously taught at Appalachian State University and the University of South Carolina. Benson has been married to Karla DeVito since 1982. They have two children, a daughter named Lyric and a son named Zephyr.
Benson was born with a heart defect, necessitating heart vale surgery in October 1984, and again in 1998. He recently underwent a third surgery. He is an activist and fundraiser for heart research, and wrote the book, lyrics, and music for a play called Open Heart, starring Benson and his wife Karla, which opened and closed off-broadway in 2004.