Career
Born in Glasgow he began his professional career with Bolton Wanderers in England, but he made only made two appearances in three seasons. While at Bolton he had loan spells with Sheffield United, Carlisle United and Tranmere Rovers, and has also represented Scotland at under-21 level. Bolton Wanderers
O'Halloran started his professional career at Bolton Wanderers, regularly playing in the reserve side.
A product of the youth system, he made his début in the League Cup tie at home to Macclesfield Town on 24 August 2011, coming on as a second-half substitute for Martin Petrov. His form in the reserves prompted Bolton to offer both O'Halloran and Joe Riley new three and a half-year contracts, committing them to the club until the summer of 2015. In March 2012, O'Halloran joined Sheffield United on loan until the end of the season, and made his début for the Blades on as an 81st-minute substitute against Chesterfield in a 4–1 victory at Bramall Lane.
O'Halloran was in and out of the side for the remainder of his spell, with his final appearance for the Blades coming at Wembley for the League One play-off final in which he came on as a substitute in extra time. O'Halloran scored in the game's penalty shoot out but United slipped to defeat. In August 2012, O'Halloran joined Carlisle United on a month's loan.
However, after playing just one game, a substitute appearance against MK Dons, O'Halloran opted to return to Bolton, his loan only lasting 12 days. O'Halloran then joined Tranmere Rovers on loan on in November of the same year. O'Halloran scored the first professional goal of his career on 8 December as he scored in a 2–2 draw against Portsmouth, O'Halloran loan was extended by a further month on 7 January 2013, and then again until the end of the season on January deadline day.
St Johnstone
After appearing in just two cup matches in three years at Bolton, O'Halloran made the move back to his native Scotland with St Johnstone in January 2014, signing an 18-month contract with the club. He scored again in Saints' final home game of the season, to conclude a 3–3 draw with former club Celtic. St Johnstone rejected two bids from Rangers for O'Halloran in January 2016.
Manager Tommy Wright then left O'Halloran out of their following league game, saying that O'Halloran was not "mentally ready" to play. O'Halloran made his final appearance for the club in a 2-1 defeat to Hibernian in the Scottish League Cup semi final at Tynecastle. Rangers
On 1 February 2016, O'Halloran signed a 4 and a half year contract with Scottish Championship club Rangers for a fee rumoured to be £500,000 on the final day of the January Transfer window.
He made his debut for the Ibrox club as a substitute in a 1-0 victory against Raith Rovers at Stark's Park on 2 February 2016. He scored his first goal for the club in a 1-1 draw with Alloa Athletic on 13 February 2016.
