His first marriage was to Tui Rererangi Walsh, with whom he had two children, Dominic O'Sullivan (1970) and Deirdre O'Sullivan (1973).
He attended St Joseph's Primary, Grey Lynn, and Sacred Heart College, Auckland which is catholic school in Glendowie He graduated from the University of Auckland and Oxford University and lectured at Victoria University of Wellington (1963–66) and the University of Waikato (1968–78).
He served as literary editor of the NZ Listener (1979–80), and then (1981–87) won a series of writer’s residencies and research fellowships in universities in Australia and New Zealand: Victoria (Wellington), Tasmania, Deakin (Geelong), Flinders (South Australia), Western Australia and Queensland.
These were interrupted by a year as resident playwright at Downstage Theatre, Wellington (1983).
In 1988 he resumed his academic career at Victoria University of Wellington, where he was Professor of English Literature until his retirement in 2004.He lives in Dunedin.