Robin Williams died in an apparent suicide by hanging, according to Lt. Keith Boyd, chief deputy coroner for Marin County Sheriff's Office.
Williams' personal assistant found the 63-year-old actor clothed, with a belt around his neck in the bedroom of his home in an unincorporated part of Tiburon, California, Boyd said. Williams also had recent "superficial cuts" on his wrist and a closed pocket knife with possible blood on it was found near his body.
The actor's publicist, Mara Buxbaum, told ABC News that the actor had been battling "severe depression of late." Boyd added that Williams had also been seeking treatment for depression.
Jeff Bridges, Sarah Michelle Gellar and Other Stars Reflect on Working with Robin Williams
Williams was last seen alive by his wife, Susan Schneider, at 10:30 p.m. on Sunday, in their home, Boyd said.
"Mr. Williams' wife retired prior to Mr. Williams into a room in the home," he said. "It is not known exactly at this time when Mr. Williams retired for the evening but he went to a different room of the home."
The next morning, Schneider left the house, believing Williams was still asleep, Boyd added.
When the actor did not respond to knocks on his door, his assistant gained entry into the room, where Williams was discovered "suspended from the belt which was wedged between the door and the door frame in a seated position slightly suspended off the ground," Boyd said.
On a subsequent 911 call, Boyd added, "The caller was distraught and indicated at that time that it was an apparent suicide due to a hanging had taken place."
Williams was pronounced dead at 12:02 p.m. on Monday.
"Preliminary results of the forensic examination revealed supporting physical signs that Mr. Williams' life ended from asphyxia due to hanging," Boyd said.
Toxicology reports were pending.
Williams had long battled demons. In the early 1980s, he confronted his alcoholism and cocaine abuse by going cold turkey.
"The one thing that cleaned me up from that was having a kid," he told Nightline in 2011. "That's immediate. I didn't have any rehabs or groups. I just kind of took my mother's advice of vitamins and exercise. You realize, OK, now you have this responsibility, and [I] dealt with it."
In 2006, after he began drinking again, Williams went to rehab. He made another visit this past July, though a source told ABC News at the time that he had not relapsed.
"After working back-to-back projects, Robin is simply taking the opportunity to fine-tune and focus on his continued commitment, of which he remains extremely proud," his publicist said at the time.