McCormack was born in Dublin and began his career with Stella Maris. He moved to England to sign for First Division club Preston North End in December 2002 after impressing on trial, and progressed to sign a professional contract in 2003. He joined Leyton Orient of the Third Division on 29 August 2003 on a one-month loan and made the first professional appearance of his career in a 4–1 home defeat to Cheltenham Town the following day, when he replaced Billy Jones at half-time. McCormack received the first red card of his career in a 0–0 draw with Lincoln City on 13 September, after committing two bookable offences. In late September, caretaker manager Martin Ling extended McCormack's loan until 1 November. He was sent off again in a 1–1 draw with Northampton Town on 25 October. He made 11 appearances, accumulating six yellow and two red cards, before his loan expired. McCormack made his Preston debut on 6 March 2004 in a league match against Burnley, when he replaced Dickson Etuhu after 55 minutes. He made four further appearances before the end of the 2003–04 season.