Benjamin was born in New York City, New York and attended the High School of Performing Arts. He married actress Paula Prentiss on October 26, 1961 and they have two children. He graduated from Northwestern University where he was involved in many plays and studied in the famous Northwestern theater school. Benjamin is Jewish. He and his wife appeared together in the short-lived television series He & She (1967-68), as well as the film Catch-22 (1970). In 1978, he starred in the ambitious, but short-lived, television series Quark.