The Dutch midfielder headed home two minutes into stoppage time to cancel out Seko Fofana's second-half opener and put PSG on 42 points from 17 games.
Mauricio Pochettino's side, who once again looked severely short of ideas, lead second-placed Marseille by 13 points after OM slumped to a 1-0 defeat at home against Brest earlier on Saturday.
Lens, who missed several chances to wrap it up before Wijnaldum's equaliser, stayed fifth on 27 points.
But it was Lens who dominated, with opportunities through Jonathan Clauss and Arnaud Kalimiuendo before the interval.
The hosts were rewarded in the 62nd minute when Keylor Navas's blunder allowed Fofana to score with a floating strike from just outside the box.
Seven minutes later, Pereira Da Costa's shot hit Navas's post before landing in the PSG keeper's arms as Lens continued to push.
Przemyslaw Frankowski tested Navas again at the end of a sharp counter-attack but PSG held out.
Florian Sotoca's attempt went just wide nine minutes from time and it proved to be Lens's last clear chance before Mbappe, who came on as a 70th-minute substitute, found Wijnaldum with a fine cross.
The Dutchman timed his jump to perfection to beat Jean-Louis Leca with a header that went into the top corner to give PSG their only satisfaction of the night.
On Sunday, Stade Rennais could move into second place, 11 points off the pace, if they beat bottom side Saint-Etienne at Geoffroy Cuichard.