Both sides had a host of chances in the first half, but neither were able to break the deadlock.
Jonathan Pitroipa and Chieck Diarra both had early opportunities for the home side, while Zlatan Ibrahimovic had the best of the chances for PSG, forcing a save from Benoit Costil in the Rennes goal just before half time.
The visitors took the lead in the 56th minute, as Jeremy Menez beat several defenders before unleashing a shot and beating the goalkeeper.
The home side fought hard as they looked to equalise but it was PSG who found the back of the net again deep into stoppage time, as David Beckham picked out Ibrahimovic, who headed into an open goal.
The result leaves PSG seven points clear at the top of the Ligue 1 table, while Rennes remain 10th.