Williams previously admitted he once thought he could handle his substance abuse on his own, but realised he would only kick his addiction with professional help.
Williams as disc-jockey Adrian Cronauer in "Good Morning Vietnam". Photo / AP
He said: "You can't [deal with it on your own]. That's the bottom line. You really think you can, then you realise, I need help, and that's the word ... It's hard admitting it, then once you've done that, it's real easy."
He had been busy working on the upcoming movie Night at the Museum: Secret of the Tomb, which was expected to hit screens later this year.
Representatives said Williams was battling severe depression, Sky News reported today.
Williams married graphic designer Susan Schneider in 2011. She was his third wife.
His first marriage was to Valerie Velardi and they had a son, but the marriage fell apart after he had a public spat with a cocktail waitress over what she said was an affair.
A year later, in 1989, he married Marsha Garces and they had two children, but divorced in 2008.
Robin and Marsha Garces Williams in 2007. Photo / AFP
Robin Williams was born on July 21, 1951, in Chicago, Illinois. His father was a senior executive at Ford and his mother was a former model.
After honing his comedic style at the prestigious Juilliard performing arts school in New York he starred in the hit TV comedy Mork and Mindy. That was followed by movies including Popeye, Good Morning Vietnam, Mrs Doubtfire and Hook, and a career in stand-up comedy including his one-man show.
Where to get help
• Lifeline: 0800 543 534
• Suicide Crisis Helpline: 0508 828 865
• Youth services: (06) 3555 906
• Youthline: 0800 376 633
• Kidsline: 0800 543 754 (4pm to 6pm weekdays)
• Whatsup: 0800 942 8787 (1pm to 11pm)
• The Word
• Depression helpline: 0800 111 757 (24-hour service)
• Rainbow Youth: (09) 376 4155
• CASPER Suicide Prevention
If it is an emergency and you feel like you or someone else is at risk, call 111.
- Bang! Showbiz