O'Hanlon began his playing career at Middlesbrough in 1982. He then joined Rotherham in 1985 and stayed there for six years, before leaving for Carlisle. Two years later he joined Preston although he was only at Deepdale for one season before joining Dundee United in Scotland. He returned to Preston in 1996, making a further fourteen performances.
Upon retirement from playing he joined the coaching staff at Preston becoming David Moyes' assistant in 1998. He was made caretaker manager in March 2002 after Moyes' departure to Everton, Moyes offered O'Hanlon a position with Everton but he chose to remain at Deepdale, initially as caretaker manager and subsequently as a permanent appointment. In June 2003, O'Hanlon left Preston due to cost-cutting measures and was appointed as a coach at Bury in January 2004, leaving in May 2005, again due to cost-cutting measures. O'Hanlon took up a part-time position in February 2006 with Chester before being appointed as coach at Barnsley in January 2007 where he remained until September 2009 when manager Simon Davey was sacked.
He was appointed first team manager at non-league club AFC Fylde in December 2009 having been assisting as first team coach for three months prior to this. He left the club in October 2011.