No cause of death has been confirmed, but police say the death may be drug-related. Ledger was 28.
Ledger was found by his housekeeper at about 3.26 p.m. ET at the apartment in the upscale Soho neighbourhood where he lived, according to NYPD spokesman Paul Browne.
The housekeeper was looking for him to let him know his masseuse had arrived.
Ledger, born in Perth, Australia, earned an Academy Award nomination and won a Golden Globe for his role as a gay cowboy in Brokeback Mountain.
He began acting in amateur theatre at age 10 and at 16, moved to Sydney, where he began acting in TV.
Ledger made his film debut in the 1997 Australian movie Blackrock and went on to make films such as 10 Things I Hate About You and Ned Kelly, about a notorious Australian outlaw.
He became a known as a heartthrob with 10 Things and A Knight’s Tale, but secured a reputation as a serious actor with his turn as Billy Bob Thornton’s troubled son in Monster’s Ball.
Ledger was engaged to actress Michelle Williams, his co-star in Brokeback Mountain and they have a daughter, Matilda Rose, born Oct. 28, 2005.
However, last September, Ledger’s father reported the couple had separated.
He was scheduled to to appear as the Joker this year in The Dark Knight, a sequel to 2005’s Batman Begins that recently finished filming.
The following was reported by CBC News