Laurent Blanc's team secured the championship shortly before kick-off after second-placed Monaco were held to a 1-1 draw by En Avant Guingamp.
The result left PSG, on 83 points, with an unassailable seven-point lead at the top of the standings.
"It was important to confirm what we did last season," midfielder Blaise Matuidi said.
"It's the result of our hard work. It's sad we did not win today but all dreams are not perfect," said goalkeeper Salvatore Sirigu.
"The first 10 months were good but the last month was not good," captain Thiago Silva said as the players' children played football on the pitch.
"I am proud of the players. We brought the title, it rewards the good work of all the staff and our ability to quickly apprehend the squad," Blanc, who took charge after Carlo Ancelotti left at the end of last season, told Canal Plus.
"I did not want to watch the Monaco game but there is always someone to tell you the result. My pre-game chat lasted 10 seconds," he said, Blanc refused to officially confirm whether he had extended his contract until 2016.
"You will know soon," he said.
PSG, who also won the Coupe de la Ligue this season, needed Guingamp to snatch at least a point at Louis II to be crowned champions without kicking a ball.
Dimitar Berbatov headed home from point-blank range to open the scoring for Monaco in the 77th minute, only for Fatih Atik to level five minutes from time.
The result triggered scenes of celebration at the Parc des Princes a few minutes before the kick-off of the PSG v Rennes game.
Guingamp, who beat Rennes in the Coupe de France final last Saturday, are 16th in the standings, two points above safety.
PSG, knocked out in the Champions League quarter-finals as they were last year, claimed the Ligue 1 lead in October after thrashing Bastia 4-0 and never surrendered it.
Monaco will finish second while Lille and St Etienne will battle it out for third place in the last two round of matches.
There were a few boos at halftime at the Parc des Princes after goals by Foued Kadir and Paul-Georges Ntep gave Rennes a 2-1 lead.
Ezequiel Lavezzi opened the scoring for PSG on three minutes after being set up by Edinson Cavani.
Kadir beat Sirigu with a low cross shot in the 23rd minute and Ntep's free kick sailed past the Italian keeper.
The crowd's discontent changed to pure joy as striker Zlatan Ibrahimovic made his comeback from a five-week injury layoff when he came on for Lavezzi in the 56th minute.
The Swede forced Benoit Costil into a spectacular save with a 40-metre strike but he failed to add to his 30 league goals this season.
PSG defender Alex had the best chance to equalise in stoppage-time but his header crashed against the bar.
The result meant that Rennes, now 13th with a six-point lead over 18th-placed Sochaux, have secured their place in the top flight as bottom clubs Evian Thonon Gaillard and Sochaux, 17th and 18th respectively, must still play each other.
- Sports & Recreation
- Laurent Blanc