Mauricio Pochettino's men had already wrapped up the title well before the visit of Les Grenats, but the Argentine's side were still in ruthless form in the capital.
Meanwhile, with 31 minutes on the clock, Neymar - who was back from a domestic suspension - pounced on a loose ball to chip over the onrushing Marc-Aurele Caillard for PSG's third goal.
By finding the back of the net against Metz, Neymar has now become only the third men's player in history to score 100 goals for three different clubs.
The Brazil international previously tallied 105 strikes for Barcelona after making the net ripple on 136 occasions during his time at boyhood club Santos.
Only Ronaldo and Romario had previously done so, with the former notching 450 goals for Real Madrid, 118 for Manchester United and 100 for Juventus.
Romario, meanwhile, amassed 128 goals for PSV Eindhoven, 184 across his two spells for Flamengo, and a total of 266 during his multiple stints at Vasco da Gama.
Despite being plagued by injuries throughout the campaign, Neymar ends the 2021-22 season with 13 goals and eight assists to his name from 28 outings in all tournaments.
As well as notching up a century of goals in his 144 games for PSG, the former Barcelona and Santos man has also set up his teammates on 60 occasions.
The 2021-22 Ligue 1 title represents Neymar's 12th major honour for PSG, with the attacker now boasting four French top-flight medals, three Coupe de France crowns, three Trophee des Champions titles and two Coupe de la Ligue triumphs.
The South American has often been the target of boss from his own supporters throughout the campaign, though, and he has been strongly linked with a move elsewhere over the past 12 months.
However, Neymar remains under contract at the Parc des Princes until the summer of 2025, and PSG can trigger a one-year extension based on his performances. body check tags ::