Professional O'Halloran began his professional football career with
Derby County in 2000 but after a promising start, starring for the youth team including a memorable individual goal in the FA youth cup against
Aston Villa and featuring regularly for the reserves he never featured in the first team. In late 2002 he spent over a month on loan at
Burton Albion scoring the winner on debut in a 2-1 win away at Nuneaton.
Grimsby Town and
Hartlepool United were linked with a move for O'Halloran in May 2003 where he spent 3 weeks on trial with the club.{{cite news He signed for
Oldham Athletic on a non-contract basis at the start of the
2003–04 season, which was extended for another month in September 2003 with the highlight being his last minute winner against
Rushden and Diamonds in a 3-2 win.{{cite news
Non-league O'Halloran signed for
King's Lynn in March 2005 following becoming disillusioned with professional football and became an integral part of the team that challenged for the Southern Premier league title where he was joined by former
Boston United teammate
Dean West. He also played a prominent role scoring important goals in the clubs FA cup run in the 2006/2007 season, culminating in their 2nd-round game being televised live on Sky Sports against his former club
Oldham Athletic eventually losing 2-0. .{{cite news He left Corby at the end of the 2008–09 season and joined his home town club
Lincoln United alongside former Boston and King's Lynn teammate
Steve Melton becoming a regular on the scoresheet from midfield. In October 2010, he joined
Lincoln Moorlands Railway but persistent concerns with an ongoing back injury resulting in ruptured discs continued and he was forced to retire from competitive football at the age of 28.{{cite web ==Notes==