Kylian Mbappe bagged a double for his first goals of the year with Neymar and Mauro Icardi also finding the back of the net after Montpellier keeper Jonas Omlin was sent off early in the opening half.
The win put PSG, who welcomed coach Mauricio Pochettino back on the bench after he was forced to spend a week in isolation following a positive coronavirus test, on 45 points from 21 games.
Montpellier are 11th on 28 points.
At the Parc des Princes, Omlin was sent off after only 19 minutes for bringing down Mbappe just outside the box.
Neymar doubled the tally on the hour with a crossed shot from Mbappe's pass. A minute later Icardi made it 3-0 from point-blank range from Alessandro Florenzi's cross.
Icardi then slipped the ball to Mbappe at the end of a counter attack for the French forward to add to Montpellier's woes.
Pochettino said he was relieved to be back on the side of the pitch.
"I feel good, I happy to be here in front of you," the Argentine told a news conference.
"It was a good game. Today we picked that combination [Mbappe, Neymar, Di Maria, Icardi]. We'll see in the future if we stick to it."
Second-placed Lille will move level on points with PSG if they beat Rennes away on Sunday.