Bayler was born in Wanganui, the son of Amy (née Allomes) and Harold Bayler, a stagehand. His first film appearance was a starring role in New Zealand film Broken Barrier (1952). Since then, Bayler has spent the majority of his six-decade long acting career in England, although he also appeared in 1981 New Zealand feature Pictures and BBC mini-series The Other Side of Paradise (1992), filmed partly in Raratonga.
Broken Barrier was the only locally made feature shot in New Zealand during the 1950s. Bayler starred as a young journalist who falls in love with a Maori woman. The film won healthy audiences in hits home territory. It was directed by Roger Mirams and John O'Shea - O'Shea went on to direct the only New Zealand feature films made in the 60s, drama Runaway and musical Don't Let it Get You.
Bayler was given stitches above an eye after he was injured in a sword fight with actor Jon Finch (playing Macbeth) during the shooting of Roman Polanski's 1971 film of Shakespeare's Macbeth. Bayler played Macduff.
Bayler's associations with Monty Python date from 1975 when he appeared in Eric Idle's BBC TV series Rutland Weekend Television. This led to his appearance as Leggy Mountbatten, manager of fictional Beatles-parody band The Rutles, in American-made TV movie All You Need Is Cash (1978). Idle also cast him in his play Pass The Butler.
He played the Bloody Baron in the Harry Potter films. He also has a small role as Mr. Gregory in Monty Python's Life of Brian (1979), and plays Lucien in Python member Terry Gilliam's third directorial effort, Time Bandits (1981).