Benedict was born in Burbank, California. He has lived and worked in Europe since the 1960s. His theatrical credits include The Rocky Horror Show in the Kings Road in the early 1970s, Harold Pinter's production of Sweet Bird of Youth, The Reverend Lee in The Foreigner and Riccardo in Franco Zeffirelli's production of Filumena in which he played opposite Pierce Brosnan in the latter's first stage role, and Bill Wilson, co-founder of Alcoholics Anonymous,in a touring production of "One Day at a Time". In 2013 he appeared opposite Steven Berkoff and Andree Bernard in the world premiere of the former's one act play An Actor's Lament at The Berkoff Performing Arts Centre at Alton College, followed by a second performance at The Sinden Theatre, Homewood School, Tenterden in Kent, two nights at The Maltings Theatre & Cinema in Berwick-upon-Tweed and then a three-week run at the Assembly Hall in Edinburgh as part of the Edinburgh Festival Fringe. In May 2014, it was revived with a short run at the Theatre Royal, Margate with a further one-week run scheduled at The Gaiety Theatre, Dublin, in September 2014.

His first film role, at the age of 11, was in the 1963 Tony Saytor film La Bande à Bobo. In 1977 he played Deak in the Tosche Station scenes in Star Wars Episode IV: A New Hope which were deleted from the film before release. Subsequent film appearances include the extended, "Special Edition" version of Aliens (Russ Jorden), The Dirty Dozen: Next Mission (Didier le Clair), Icon (Carey Jordan), The White Knight (Turkish Ambassador), The Russia House (Spikey), Saving Grace (the MC) and Rewind. In 2003 he was third lead in Vicente Aranda's version of Carmen, playing Don Prospero.

He has also appeared widely on television, most notably as Frank Crowe in an episode of the BBC's award-winning 2003 docudrama television miniseries Seven Wonders of the Industrial World, John E. Jones III in Nova's Judgment Day: Intelligent Design on Trial, Alan Kalanak in the 2001 Christmas Special edition of Jonathan Creek and Yves Houdet in Thames Television's mini-series of Angus Wilson's Anglo-Saxon Attitudes. Other television appearances include Lilyhammer as Agent Becker, Queen Victoria's Men (Lord Melbourne), Sharpe's Honour (General Verigny), Bergerac (Martin Colley), Emmerdale (Doug Hamilton), Death Train (Halloran), Harnessing Peacocks (Eli Drew) and Only Love (Roger). He provided the voice for Shiro Hagen in Star Fleet, the English adaptation of the Japanese X-Bomber.

In August 2014, he returned to the Edinburgh Festival Fringe to play Archie Bellows in the world premiere of Terry Jastrow's "The Trial of Jane Fonda", opposite Anne Archer, playing World War II veteran Archie Bellows.