Irishman O'Halloran, who has represented his country all the way from u-15 level to full honours, started off his footballing life with Springfield Ramblers, the youth arm of Cobh Ramblers in the Republic, before joining Aston Villa's youth academy in the summer of 2003 at the age of 15, O'Halloran then going on to earn a professional deal with the Villains, although he never made any first-team appearances in seven years with the Premier League club.
Loan spells were aplenty though starting with a three-month one at League Two Wycombe Wanderers from October 2006 to January 2007 in which he made 12 starts and two substitute appearances. His next period away from Villa Park coming, as he bided his time playing for Villa's reserve side, in February 2008 although he only made one substitute appearance for Southampton in the Championship before he returned back to his parent club.
He was soon out on the road again but a loan spell at the end of that month was extremely abrupt as he suffered an anterior cruciate ligament injury at Swindon in the warm-up for what would have been his Leeds United debut in League One. Back fit again in November 2008 it was then off to Swansea for a three-month loan spell in the Championship but just a month and three starts later he picked up another anterior cruciate ligament injury.
In mid-June 2010 the Cobh-native finally left Villa for good though as he signed a one year contract with an option for a further year with Championship side Coventry City. His next injury was soon round the corner however when he slipped a disc in his back during a pre-season game at Nuneaton, his Sky Blues debut therefore coming in late December last year as a substitute in a 2-0 home defeat against QPR, that only O'Halloran's fifth appearance in 3 years and 11 months at senior level.
Since that point the left-sided defender made 10 starts for Coventry before losing his place to the fit again Chris Hussey after a couple of months and eventually being released at the end of last season, having made another couple of starts in Hussey's absence, by Sky Blues boss Andy Thorn. O'Halloran now linking up with the Cumbrians for the start of Brunton Park pre-season training at the end of next week as he looks to earn a permament deal and offer some competition against current United first choice left-back Matty Robson.