Heath Ledger was found dead in his bed at his apartment on Broome Street, Soho in Manhattan, by his housekeeper at 3.35pm local time.
He has died of a possible drug overdose involving sleeping pills in New York, police have confirmed.
He was pronouced dead at 3.45pm (7.45am AEDT) by a medical examiner who went to the apartment.
US television network NBC reported his body was found surrounded by pills.
The New York Times reported Ledger was discovered by a masseuse who arrived at his apartment for an appointment. The masseuse was let in to the home by a housekeeper, who then knocked on the door of Ledger's bedroom, The New York Times reported.
When no one answered, the housekeeper and the masseuse opened the bedroom and found Ledger unconscious. They shook him, but he did not respond. They immediately called the authorities. The police said they did not suspect foul play.