She died at the Cairns Base Hospital in Queensland, Australia late on Thursday, according to the Australian Broadcasting Corporation (ABC).
Cilento was born into a medical family in Mooloolaba, Queensland, in 1933 and went on to train at the Royal Academy of Dramatic Art in London in the 1950s.
She secured work on stage and in film, and earned a supporting actress Academy Award nomination for her portrayal of Molly in the 1963 picture "Tom Jones."
The movie won best picture and best director for Tony Richardson.
In 1962 she married Sean Connery, her second marriage, and had a son, Jason, with him before the couple divorced in 1973.
Cilento married for a third time in 1985 to Anthony Shaffer, who wrote "Sleuth" and "The Wicker Man," a film in which she also appeared. Shaffer died in 2001.
In the 1980s she established the outdoor theater the Karnak Playhouse and wrote an autobiography "My Nine Lives" in 2006.
ABC quoted friend and playwright Michael Gow as saying he was with Cilento at a dinner party last weekend.
"She was a performer to the end, and she put on a great display for all the guests at that dinner," he was quoted as saying.
"She kept us all hugely entertained until the day before yesterday, when she just couldn't manage anymore and we took her to hospital."
No cause of death was given.
-- Reuters contributed to this report.
– The Hollywood Reporter