Filed by an unidentified freelance reporter, the lawsuit accuses photographers Eric Munn and Darren Banks of approaching the "Brokeback Mountain" star in 2006 at Hollywood's Chateau Marmont Hotel and offering him cocaine, the New York Daily News reported Saturday.
The suit alleges Ledger, who died early this year of an apparent overdose, had his own cocaine and started using the drug with Banks.
While the pair was snorting the cocaine, Munn secretly began filming the scene until Ledger discovered what was taking place, the suit alleges.
"Mr. Ledger became aware that he was being videotaped and became very upset," the suit alleges "He realized the two men he had been befriending all evening were paparazzi."
The suit said the two Splash news agency employees allegedly sold the video to "Entertainment Tonight" despite telling Ledger they would destroy it.
The Daily News said the reporter is seeking unspecified damages in the suit.