Roberts was born in Manhattan, New York City, the son of Norma (née Finkelstein), an Animator, and CBS radio announcer Ken Roberts. His family is Jewish. He had a sister, Nancy, and is the cousin of late actor Everett Sloane. Roberts attended The High School of Music & Art and Northwestern University, and made his Broadway debut in 1962, with a role in the play Something About a Soldier.
On television he has appeared in numerous series such as The Carol Burnett Show, Matlock, and Law & Order. In 1977, he starred in the short-lived series Rosetti and Ryan with Squire Fridell. In 1978 he guest starred on The Love Boat where he and Lauren Tewes' character, cruise ship Director Julie McCoy, fell in love but didn't pursue a relationship. (Roberts' character, a widowed father of two girls, eventually married someone else, much to Julie's bitter regret). On radio he was a regular performer on the CBS Radio Mystery Theater. Roberts also provides the narration on many, if not all, of the audio books in the Stone Barrington novels written by Stuart Woods.
Roberts memorably portrayed the badgering Deputy Mayor Warren LaSalle in The Taking of Pelham One Two Three. He also appeared in the Sidney Lumet films Serpico and Just Tell Me What You Want. Roberts was in the 1983 horror film Amityville 3-D portraying John Baxter, the owner of the infamous possessed house.
Roberts' Broadway credits include Barefoot in the Park; How Now, Dow Jones; Murder at the Howard Johnson's; Promises, Promises; Sugar (the musical version of the movie Some Like It Hot); The Sisters Rosensweig; They're Playing Our Song; Victor/Victoria; The Tale of the Allergist's Wife; Arsenic and Old Lace; and Cabaret. In 1998 Roberts played the role of "Buddy Plummer" in Stephen Sondheim's Follies at the Paper Mill Playhouse in New Jersey. In May 2007, Roberts returned to Broadway in the roller-disco rock musical Xanadu.
Roberts was featured in 2014's The Longest Week opposite Jason Bateman.
