The former Chelsea midfielder, who helped Saints win promotion last season, was in the final year of his previous deal. Morris has impressed in the SPL this season and the 30-year-old had been linked with a move away from McDiarmid Park.
He said: "I'm happy here, enjoying my football and we have a tight-knit dressing room. I've had a new lease of life since coming to St Johnstone two years ago and I'm loving the SPL."
Saints manager Derek McInnes added on the club's official website, www.perthstjohnstonefc.co.uk: "I'm delighted that the club and Jody have been able to tie this up. He has been a real asset to us since he joined and he is a huge influence on the rest of the squad."
McInnes insists his St Johnstone team will put aside dreams of cup glory to concentrate on crucial league points when they welcome rock-bottom Falkirk to McDiarmid Park today. The Perth men won through to their fourth major cup semi-final in four years with a 2-1 home win over Dundee United in the Co-operative Insurance Cup on Tuesday night.
However, a victory for struggling Falkirk would actually see them leapfrog St Johnstone, who are only two points ahead.
"No team has greater need for points than us," argued McInnes. "We are in desperate need of a win because we have nowhere near enough points yet."
Meanwhile, Alex MacDonald is determined to fire Falkirk off the bottom after responding to manager Eddie May's fitness warning.
The on-loan Burnley striker is set to face St Johnstone, having made his first start since August during last Saturday's goalless draw at Hearts.
The 19-year-old's return followed a heart-to-heart with May when he was told to improve his stamina and lifestyle. MacDonald responded by adapting his diet and undergoing individual training sessions with coach Steven Pressley to shed pounds and get back in the manager's plans.
"Previously he wasn't in any physical condition to start a game," said May, who is still looking for his first domestic win.
"We pointed that out to him. To his credit, he has come back in good condition – and we're seeing the benefit on the park."
MacDonald said: "It's brilliant to be back playing. I needed to get fitter. It was just me and 'Elvis' at times out there. He has worked me very hard, and now I'm seeing the benefits."