Boyle wasn't always an actor, he pursued acting only after he left the life of a monk. His successful career includes his roles in films like The Candidate, Young Frankenstein, Monster's Ball and Where the Buffalo Roam (a portrait of Hunter S. Thompson, in which he played Carl Lazlo, Esq.). While he was living in Chicago in 1968, he witnessed the chaos and violence at the Democratic National Convention, and later described himself as a “conservative radical.” He also stated he would not act in movies that glorify violence.
During the filming of Young Frankenstein he met Laraine Alterman, who was on the set interviewing Mel Brooks for Rolling Stone magazine. Boyle married Alterman in 1977, his good friend John Lennon was best man at their wedding.
Boyle suffered from multiple myeloma and heart disease. Alterman survives him with their two daughters.