When no one answered, the housekeeper and the masseuse opened the bedroom and found the actor unconscious on a bed, naked, surrounded by prescription medicine and another non-prescription drug.
The housekeeper and masseuse shook Ledger, but he did not respond. They then called the authorities, according to police.
Police added that they did not suspect foul play. Initial reports claimed actress Mary-Kate Olsen owned the apartment Ledger was found in, but police denied that the residence was Olsen's. A police source later said the maid or the housekeeper called Olsen and her security team responded to the apartment on Broome Street.
They said it was not clear who owned the apartment, but Ledger appeared to be a resident.
The superintendent of the building, Tamba Mossa, told ABCNEWS that Ledger had "been renting the apartment for about four months" but he didn't know who owned the residence. Mossa added that he was surprised to learn about Ledger's death, saying the actor had always been "very nice" and would often go on walks with his young daughter.
Ledger's publicity agency told ABCNEWS Tuesday that it "had no comment at this time."
Police said an autopsy will be performed on Wednesday.
The Australian-born actor is probably best known for starring in 2005's "Brokeback Mountain," about two cowboys who fall in love. He earned Oscar, Golden Globe and Screen Actors Guild nominations for that role. He also met actress Michelle Williams while filming the movie. The couple had a very public romance, and a daughter, Matilda Rose, in October 2005.
In September 2007, Ledger and Williams separated. Ledger was rumored to be dating British model Gemma Ward shortly before his death.
Later this year, Ledger is slated to appear as the Joker in "The Dark Knight," the latest film in the Batman franchise. In a November interview with The New York Times, he revealed how he'd thrown himself into the role, saying, "Last week, I probably slept an average of two hours a night. … I couldn't stop thinking. My body was exhausted, and my mind was still going.''
According to the newspaper, he was taking the sleep medication Ambien to get rest, but to no avail.