After winning five British titles and one world title in British & World Trampolining tournaments, he entered show business in 1980 when he appeared in the pantomime Jack and the Beanstalk, with Barbara Windsor. Sundin made various television and theatre appearances, both as an actor and dancer, which led to a long run in the Cameron Mackintosh-produced musical Cats, in which he played Bill Bailey in its West End run from 1982 until 1983. He also appeared in the video for Culture Club's I'll Tumble 4 Ya from 1982.
