His credits include parts in such films as Color Me Dead (1969), Ned Kelly (1970), The Chant of Jimmie Blacksmith (1978), The Survivor (1981) and Bush Christmas (1983), as well as a starring role in television series Spyforce along with his portrayal of Bill Hayden in The Dismissal.
In an interview in 1978 for the Sir Joseph Banks High School newspaper, he revealed that he had an uncredited role off stage, controlling the Dianoga (garbage compactor monster) in Star Wars, as well as playing the role of Lieutenant Pol Treidum in that film.
His other local television acting work included regular roles as Bruce Jefferson in Tickled Pink (1978–81), Phillip Seymour in All the Way (1988), Reverend Green in Cluedo (1992), and Les Bailey in Heartbreak High (1997–99), along with numerous guest roles in series including Homicide, Division 4, Matlock Police, Boney, The Sullivans, Cop Shop, Neighbours, E Street, The Flying Doctors, and Home and Away.
Sumner was a follower of Meher Baba and directed a TV documentary, Baba's Birthday, shot in India, produced by Sensory Image, with music by Pete Townshend.
[2] Sumner also served a stint as a presenter on Play School, mainly acting as a stand-in for John Hamblin.