The 25-year-old forward, who joined Rangers from St Johnstone in the January transfer window, started his career at Celtic.
O’Halloran was at the Bhoys as a kid, but he failed to progress to the first team and moved to Bolton Wanderers.
Things did not work out for Scotsman at Bolton either, and he joined St Johnstone in 2014.
It is not easy to cross the divide between Celtic and Rangers, but O’Halloran has said that he did not find it tough.
“It [crossing the divide] wasn’t a concern at all,” the former Scotland Under-21 international told The Daily Record. “It didn’t bother me and it has been great so far. I did play against Rangers as a Celtic youth player.
“A couple of the boys, including Danny Wilson, are in the dressing room here now. Everyone has been really welcoming so far – I’m really enjoying it.”
Rangers are at the top of the Scottish Championship table at the moment with 72 points from 29 matches.
Mark Warburton’s side are 11 points clear of second-placed Falkirk and have a game in hand.
The Gers are set to get automatic promotion to the Scottish Premiership at the end of the season.