Glasgow-born O’Halloran joined Saints from Bolton Wanderers in January 2014 , scoring 10 goals in the last Premiership campaign to help the club finish fourth to qualify for Europe for a second year, after being part of the historic, first 2013/14 Scottish Cup-winning side.
He said: “Obviously I’m delighted to sign a contract extension at the club.
“It wasn’t a hard decision to make because the management have been good to me and it’s a great set of lads in the dressing room, who are all as hungry as I am to build on the success we’ve had at the club in the last few seasons.
“I feel I’ve developed and grown as a player at St Johnstone, because I’ve been playing week in, week out here. That’s really important to any player to help you learn and develop.
“This season we want to go as far as we can in Europe, which realistically means reaching the group stages of the Europa League.
“It would be great to go a little bit further than we did last season to get there. Retaining our place in the top six and doing well in the cup competitions have to be our other targets after that.
“I’d like to thank the Saints fans for all the support they’ve given me since I joined. They’ve been absolutely brilliant towards me and I really can’t speak highly enough of them.
“We’ve got important European games coming up so it would be great to see them out in the numbers they did last season. It really does make a difference.”