Anne de Peyster, formerly Anna Murdoch, died in Palm Beach, Florida, following a long illness, according to reports in the Murdoch-owned New York Post.
In its coverage of her death, the paper said "many worlds loved Anna".
"Devoted mother, handsome lady, sharp wit, love of writing and lifetime commitment to helping children in need."
Ms De Peyster married real estate developer Ashton de Peyster in 2019, having divorced Rupert Murdoch two decades earlier.
Born in Scotland the eldest of four children in 1944, Ms de Peyster moved with her family to Sydney as a child.
Raised a Catholic, she attended Our Lady of Mercy College at Parramatta before finding work as a journalist.
She and Mr Murdoch married in 1967 after he divorced first wife Patricia Booker.
After working at both Sydney's Daily Mirror and Daily Telegraph, Ms de Peyster eventually served on the board of Murdoch family company, News Corporation, for eight years.
According to her Wikipedia page citing Britain's Independent newspaper, the people who in 1969 kidnapped and killed Muriel McKay, the wife of Mr Murdoch's deputy Alick McKay, had originally intended to kidnap her instead.
Confusion arose when the McKays used of one of Murdoch's vehicles.
Following her divorce from Mr Murdoch, Ms de Peyster reportedly received $1.7 billion, including $110 million in cash, from the settlement.
Ms de Peyster had a Master's degree in literature wrote three novels: In Her Own Image, Family Business and Coming to Terms.
She was also a noted philanthropist and socialite in Palm Beach and Southampton.
Ms de Peyster was also married for 17 years to financier William Mann.
She is survived by Mr de Peyster, her three children, 10 grandchildren and one great-grandchild.
According to the New York Post, she died on Tuesday, surrounded by family.
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