[1] Born of Ngāti Kurī and Te Aupōuri descent, Selwyn grew up in Taumarunui and began his professional life as a teacher.

In 1967 Selwyn acted in The Golden Lover at Downstage Theatre directed by Richard Campion alongside Wi Kuki Kaa and Bob Hirini.

[2] Also on stage produced by Downstage Theatre and directed by Campion and designed by Raymond Boyce, Selwyn was in Othello with a cast of 17 including Peter Vere-Jones and Elric Hooper in 1976.

In 1984 he began a film and television training course for Māori and Pacific Islanders He Taonga i Tawhiti (Gifts from Afar).

[9] In the 1999 New Year Honours, Selwyn was appointed an Officer of the New Zealand Order of Merit, for services to theatre, film and television.