The on-loan Rangers marksman has endured a miserable campaign due to a persistent ankle complaint but was in the right place at the right time to hammer home a cathartic strike against his former club.
The 21-year-old’s clinical finish completed a superb turnaround from Gary Holt’s men, who had fell behind courtesy of an Alfie Jones header before Scott Pittman levelled after the break. Craig Sibbald added late gloss to the triumph with his first goal for the club.
While the Lions roared back into the top six, St Mirren will now find themselves rock bottom of the Premiership if Dundee avoid defeat against Rangers on Sunday.
Only Celtic and Rangers had collected more points at home that Livi this season prior to kick-off, and Gary Holt’s men started brightly as Steven Lawless lashed a powerful drive narrowly over the bar.
However, any early momentum was lost when a nasty clash of heads between Paul McGinn and Craig Halkett resulted in a delay of several minutes while the full-back received treatment. With the experienced defender visibly dazed, he was rightly replaced my Matthew Willock.
And it was St Mirren who would emerge from a forgettable opening period with an advantage as Jones met a wonderful delivery from Adam Hammill to head home his first goal since joining the Buddies on loan from Southampton.
Livingston emerged from the interval like a team who had been read the riot act by boss Holt and were level within six minutes of the restart, with Pittman unleashing a ferocious low shot from the edge of the box beyond the despairing dive of Danny Rogers.
With their tails up, Livi claimed the lead after 64 minutes when another effort from Pittman was blocked, only to fall perfectly into the path of Hardie - who lashed into the roof of the net from point-blank range.
Livi almost put the game to bed when a deep delivery was only cleared as far as substitute, Jack McMillan - but the youngster’s looping header struck the crossbar and bounced into the grateful arms of Rogers.
However, that would prove a fleeting let-off for the Paisley outfit as Sibbald pounced on a spilled Pittman drive after 88 minutes to complete the scoring with a tap-in.