 O'Sullivan was first elected to Dáil Éireann at the 1989 general election as a Labour Party Teachta Dála (TD) for Cork North-Central having topped the poll.He was re-elected at the 1992 general election, receiving 10,008 first preference votes, again topping the poll.He served as Minister of State at the Department of the Marine (with special responsibility for Port Development Safety at sea and Inland Fisheries) from January 1993 until his death following a short illness in August 1994.