Pittman finished at the far post in the 56th minute to maintain Livingston's position in fifth place in the Ladbrokes Premiership and ruin Tommy Wright's 300th match in charge of Saints.
Rangers goalkeeper Robby McCrorie twice saved well from Michael O'Halloran to earn a clean sheet on his debut after swapping his Queen of the South loan spell for Livi in the wake of Ryan Schofield picking up a thigh injury on his first appearance.
Both sides came into the game in form with Livi losing just once in eight games and St Johnstone letting in only one goal in their previous six outings.
The teams were predictably evenly-matched with neither goalkeeper troubled in the opening half hour, although Saints claimed for a penalty when O'Halloran went down under pressure from Ciaron Brown.
The hosts came closest to breaking the first-half deadlock when Stevie Lawson curled a 20-yard free-kick off the outside of the post.
Saints had their best opening of the half seconds later when O'Halloran won the ball off Brown and got in behind after a one-two with Stevie May, but McCrorie stopped his shot from a tight angle and saved Jason Holt's follow-up.
Livingston wide man Stevie Lawless was causing problems but it was two centre-backs that almost fashioned the opener in stoppage-time, Jon Guthrie heading wide of the near post from Brown's deep cross.
Saints goalkeeper Zander Clark made his first save just after the break when he brilliantly pushed over Pittman's 22-yard strike.
The visitors broke moments later and McCrorie made a close-range stop from O'Halloran after Drey Wright's cross.
The breakthrough came after the home side worked the ball to Lyndon Dykes following a throw-in on the left. The striker drove a cross to the far post and the unmarked Pittman converted first time just inside the post from 10 yards.
Clark soon made another stop from a Pittman long-range effort and Saints were struggling to get back in it before Wright made a triple substitution with 20 minutes left.
Full-back Scott Tanser came on along with strikers Chris Kane and Callum Hendry as Saints switched to a 3-4-3 formation. The visitors soon threatened but Brown cleared O'Halloran's effort off the line and Hendry could not convert the rebound under pressure.
Clark soon saved from Dykes and Gary Holt's side saw out the win.