Two first-half goals within 30 seconds of each other from Scott Tiffoney and Alan Forrest sealed a second league win of the season and seen the Lions jump from 12th to 8th place in the table.
A cagey opening to the game made for a rather stop-start tie with neither team really taking a foot hold in the game.
Craig Conway whipped a teasing ball into the box from the right wing and Stevie May got to it first but his stabbed effort was straight at goalkeeper Robby McCrorie who had spread himself well and saved.
Conway himself would then waste a chance from the edge of the box, having done well to get away from Julien Serrano but sent the ball high over the bar.
The Lions would make the most of that let-off by securing what proved to be an unassailable lead before half-time.
Saints striker Michael O’Halloran dawdled on the ball in the middle of the park, allowing Tiffoney to nip in and rob him, before spearheading a counter-attack. He took the ball to the right of the box and squared for Forrest who checked inside but seen his first attempt blocked with the ball spinning to Scott Robinson who would tee Forrest up again and when his second effort was blocked, the ball fell kindly for Tiffoney who calmly passed the ball beyond Zander Clark and into the bottom corner.
The duo would link up again moments later to carve a superb clinching goal. Marvin Bartley picked up a loose ball in the middle of the park and drove down the left before cutting back for Julien Serrano. The French defender would cross from the left where Tiffoney cushioned the ball into the path of Forrest, who guided his finish inside the far post, putting the Lions two goals ahead for a first time this season.
That goal would be the killer for St Johnstone who struggled to get back into the game after that. A flurry of corners and long balls into the box were all swept up by a disciplined Livingston backline. Even when they did eventually beat McCrorie, with Callum Hendry curling one past the keeper, Jason Holt popped up to head off the line and keep that two-goal lead safe.
A huge three points for the Lions who now head to Tannadice on Friday night knowing that a second win on the bounce would ensure a further advance up the league table.
Livingston: McCrorie, Devlin, Ambrose, Guthrie, Serrano, Bartley ▊, Holt ▊, Robinson (⇔ Brown 77), Pittman, Forrest (⇔ Lawson 69), Tiffoney (⇔ Lokotsch 71)
Subs not used: Fitzwater, Sibbald, Poplatnik, McMillan, Taylor-Sinclair, Stryjek,
Goals: Tiffoney (34), Forrest (35)
St Johnstone: Clark, McNamara (⇔ Gordon 53), Kerr (⇔ Rooney 82), Mccart, Tanser, Conway (⇔ Wotherspoon 77), Davidson, McCann, Craig (⇔ Hendry 53), O’Halloran, May
Subs not used: Parish, Olaofe, Robertson
Referee: Craig Napier
Match Report: Dave Black