Williams was found dead at 6:15 pm on Thursday in an El Segundo hotel room, Los Angeles County coroner’s Captain John Kades said.
An autopsy will determine the cause of death. A toxicology examination will take six weeks to be completed, Kades said.
Born Mary Vesta Williams on December 1, 1957, to a disc jockey in Coshocton, Ohio, she had hits with Once Bitten Twice Shy, Sweet, Sweet Love and the torch song Congratulations, where she emotionally bids goodbye to her ex, about to marry someone else, on his wedding day.
Williams also appeared in movies and on television.
She was a saloon singer in the Mario Van Peebles movie Posse and she had a recurring role on the television situation comedy Sister, Sister, playing actress Jackee Harry’s best friend Monica.
Harry tweeted her condolences: “… just received truly devastating news: R&B great, and my friend of many yrs, Vesta Williams @vesta4u), has passed away. #RIPVesta”
Williams’ diminutive frame belied her powerful, soulful pipes. Her initial success in the music industry came as a background singer for artistes ranging from Chaka Khan, Anita Baker and Sting. But she would eventually establish her career with release of her first album, Vesta, in 1986.
Williams continued to make albums, and was a regular performer on the concert circuit.
She was to perform at the 21st annual DIVAS Simply Singing! in Los Angeles next month, put on by Singer and actress Sheryl Lee Ralph. The October 22 show will now pay tribute to her and another late soul singer, Teena Marie.
“She was really excited about doing Divas,” her friend Ralph told The Associated Press, adding that Williams was also scheduled to be the subject of a TVOne Unsung episode.
The 5-foot-3 entertainer gained weight in the 1990s, ballooning to a size 26. She went on a dramatic weight loss programme, losing 100 pounds and getting down to a size 6.
Last year, she released a song on iTunes. In an interview last December with Egypt Thompson on the Web show The Couch, she said she was blessed.