He was born Percy James Patrick Kent-Smith in Dunoon, Scotland.
He came to prominence as a member of the comedy act "The Ken Campbell Roadshow". His best known act was as a stuntman character called "Sylveste McCoy", whose stunts included putting a fork up his nose and stuffing ferrets down his trousers. As a joke, the programme notes listed Sylveste McCoy as played by "Sylvester McCoy", and after a reviewer missed the joke and assumed that Sylvester McCoy was a real person, Kent-Smith adopted this as his stage name.
Notable television appearances before he gained the role of the Doctor included roles in Vision On and Tiswas.
He took over the lead role of Doctor Who in 1987, taking over from Colin Baker, and remained the lead until the series was shelved three years later. He returned for the 1996 telemovie, where he handed the role over to Paul McGann.
His television roles since Doctor Who have included the villain in the 1997 telemovie Beyond Fear.
He has also acted extensively in theatre.