Born in Cyprus, O'Sullivan played youth football for Swindon Town before making his professional debut with the club.
O'Sullivan came on as a substitute for Republic of Ireland under-21 in a win over Latvia in 1996 UEFA European Under-21 Championship qualification on 10 October 1995.
[3] After being released by Central Coast Mariners, O'Sullivan had spent months trying to find a spot in another football team to continue his playing career, but was not successful.
[4] On Thursday, 16 My 2019, O'Sullivan was appointed as new coach for the remainder of the 2019 National Premier Leagues NSW 2 season with the Bonnyrigg White Eagles FC.
[5] To begin the 2019 CAS Football season, O'Sullivan was appointed Head Coach of the Barker College 1st XI, leading them to the title.