Lens were down to 10 players on the pitch of the Parc des Princes Stadium when Kevin Danso performed a sliding tackle and fouled PSG's Brazilian star Neymar.
Danso was shown his second yellow card and sent off in minute 57 in Paris.
PSG broke the deadlock in the 68th minute when Argentine superstar Lionel Messi scored a classy goal from outside the box.
However, Lens did not give up and scored the equalizer in the 88th minute to dispirit PSG. Lens forward Corentin Jean slid to finish in the six-yard box after a low cross taken by Deiver Machado.
PSG is guaranteed to finish the Ligue 1 on top, boosting their points to 78 in 34 matches.
Second-place Olympique Marseille have 62 points in 33 games.
The French league will end in four weeks on May 21.
Paris Saint-Germain players and fans at the stadium celebrated their league success after the match.
It was Messi's first French league title with PSG since the 34-year-old left his boyhood club Barcelona for Paris Saint-Germain in the summer of 2021.
PSG claimed their record-equaling 10th French title. Saint-Etienne also has 10 French league titles -- their last coming in 1981.
Paris Saint-Germain previously won the Ligue 1 in 1986, 1994, 2013, 2014, 2015, 2016, 2018, 2019 and 2020.
