Nunn received his medical education at the University of Adelaide, qualifying MB BS there in 1951. He came to Britain and passed the Fellowship examination in 1957, before returning to Australia, where he practised at Claremont, WA. He was staff specialist at the Royal Perth Hospital in 1959 and also at the Princess Margaret Hospital, Perth from 1959 to 1967. He died at Claremont, Western Australia, on 7 October 1993.