McCormack, subject of three failed bids from Middlesbrough, played a massive part in Leeds' equaliser after they fell behind to a great strike from David McGoldrick on 11 minutes.
The striker took aim from 25 yards and his speculative effort cannoned off Luke Chambers and into the path of Luke Varney, who made no mistake.
The goal came against the run of play as Ipswich dominated the opening stages, before the visitors matched them before half-time and then deserved their second-half winner.
And it came from McCormack as he cut inside to shoot low past Scott Loach from 20 yards.
The Town keeper could point to a slight deflection off Town midfielder Cole Skuse and the slick Portman Road pitch, but will also look at his own role in the winner.
In an entertaining start, the hosts thought they had taken the lead after just seven minutes when the highly-rated Aaron Cresswell fizzed a low cross into the area and Jay Tabb turned in McGoldrick's mis-hit shot.
But the diminutive midfielder was rightly adjudged to have been offside as he tapped in from close range.
The home fans did not have to wait long to cheer the first goal after Daryl Murphy flicked on Scott Loach's long clearance and McGoldrick left Leeds defender Tom Lees on his backside before clinically firing home off the inside of the post.
As the hosts continued to press, Lees headed a sharp Carlos Edwards corner over his own bar before a dominant Ipswich went agonisingly close to doubling their advantage.
The impressive Cresswell took aim from 20 yards out and hit the crossbar, the rebound eventually finding Tabb whose shot hit the side netting.
Against the run of play, Leeds grabbed a 28th-minute equaliser - and in fortuitous circumstances - as Varney took advantage of the deflection to finish clinically.
The visitors got off to a flying start in the second half thanks to McCormack's 20-yard strike just four minutes after the restart.
With 20 minutes left, Leeds were indebted to Noel Hunt who chested the ball off his own goal line when Luke Chambers directed substitute Paul Anderson's corner goalwards.
Ipswich toiled without truly threatening Kenny's goal.
In fact it was the visitors who looked more like adding to their tally, with Loach pushing away Hunt's shot following good work from Lee Peltier and Rodolph Austin and Paul Green's long-range shot fizzing just wide.
Luke Hyam saw a similar effort hit the side netting for Ipswich with 10 minutes left before Skuse's shot from the edge of the area deflected off Lees but wide, Smith heading the resulting corner over the bar.