It was named best film and won best director for Jacques Audiard, while Clint Eastwood's Oscar-winning "Million Dollar Baby" was named best foreign film, the BBC reported Sunday.
An honorary achievement Cesar was awarded to British actor Hugh Grant.
"I don't win a lot of prizes, especially at home," Grant said in French. "Thank you France."
Michel Bouquet was named best actor for playing the late President Francois Mitterrand in "Le Promeneur du champ de Mars (The Stroller in the Champs de Mars)," and Natalie Baye won the best actress award for "Le Petit lieutenant (The Little Lieutenant)."
The start of the ceremony was delayed for about 20 minutes by a demonstration by film workers, the BBC said. While 200 protesters demonstrated outside, a dozen activists seeking more rights for temporary employees rushed the stage.