O'Neill started his career in the Youth system at Burnley, starting a three-year scholarship in 2000. His professional debut for the club came in April 2003, coming on as a substitute for Mark McGregor in a 7–4 defeat to Watford. He made his first start in a 2–0 win over Gillingham. In June 2013, O'Neill signed his first professional contract with the club on a one-year contract. In his first year as a professional, O'Neill struggled to make an impact only making four appearances. In the summer of 2004 he signed a one-year extension to his contract. In November 2004, O'Neill played his final game for the Clarets in a 2–1 win over rivals Leeds United. In February 2005, O'Neill joined Conference National side Accrington Stanley on an initial one-month loan deal, which was later extended to two months. He made his debut for the club in a 2–2 draw with Forest Green Rovers. His only goal for the club came in a 4–3 Conference League Cup win over Northwich Victoria. O'Neill returned to Burnley in May 2005 but was however released by manager Steve Cotterill due to the expiry of his contract. In July 2005, O'Neill re-joined Conference National side Accrington Stanley after training with the club during pre-season. In August 2005, O'Neill was on the move again, joining Northern Premier League Premier Division side Radcliffe Boroughon loan until October 2005. In January 2006, he joined Radcliffe on a permanent basis after leaving Accrington. O'Neill stayed with Radcliffe for another season but the club struggled throughout the campaign and were relegated from the NPL Premier Division in 2007. He made a total of 85 appearances in all competitions during his time with Radcliffe scoring eleven goals. O'Neill remained in the NPL Premier Division with Ashton United after manager Danny Johnson had been impressed with his form at Radcliffe. He scored an incredible volley on his debut for the club in a 7–2 demolition of Frickley Athletic. O'Neill stayed with Ashton United for six years making over 170 appearances as they continued to compete in the NPL Premier Division. He also won the Supporters' Player of the Year award in 2010. In September 2013, he joined fellow NPL Premier Division side Nantwich Town, making his debut as a substitute in the FA Cup defeat to Rugby Town. O'Neill spent three months at Nantwich before dropping down the football pyramid to join North West Counties Football League First Division side Nelson. His debut for the club came in December 2013, in a 3–1 home win over 1874 Northwich. He finished the season with three goals in fourteen appearances for the Admirals as they were crowned champions and gained promotion to the NWCFL Premier Division.
