Trained with the Royal Shakespeare Company, Buck performed in the classics on-stage, but soon became a familiar presence on film and television, with his rakishly handsome looks typing him as adventurers in horror and gothic films. He appeared in the Disney TV adventure serial The Scarecrow of Romney Marsh (as young Harry Banks, with Michael Hordern as his father) and hosted the anthology series Mystery & Imagination (as Victorian gentleman Richard Beckett). Buck's movie stardom was confined to a brief spate of leading and secondary lead roles in the 1960s films The Mummy's Shroud, Deadfall (with Michael Caine), and A Taste of Excitement.
However, he branched out into writing, and soon became a prolific dramatist for BBC radio, often penning historical dramas and biographies of classical composers, with such lofty titles as The Conflict of Doves and The Image of God. He continued working as an actor behind the microphone, playing Dr. Watson in a 1978 Sherlock Holmes series; the same year, he voiced Gimli in Ralph Bakshi's animated The Lord of the Rings. His final role was for radio, as an undertaker in the ghost story The Dead Drummer, which he also penned.