Victor Dlamini, the Mandela family spokesperson, said she died peacefully in her sleep in Johannesburg hospital surrounded by her family and loved ones.
Calling her "one of the greatest icons of the struggle against apartheid", in a statement, he said she "sacrificed her life for the freedom of the country."
"Her activism and resistance to apartheid landed her in jail on numerous occasions, eventually causing her banishment to the small town of Brandfort in the then Orange Free State," he said. "She kept the memory of her imprisoned husband Nelson Mandela alive during his years on Robben Island and helped give the struggle for justice in South Africa one its most recognisable faces. She dedicated most of her adult life to the cause of the people and for this was known far and wide as the Mother of The Nation."
He added: "The Mandela family are deeply grateful for the gift of her life and even as our hearts break at her passing, we urge all those who loved her to celebrate this most remarkable woman."
Mandela is known to have been ill for a number of years and was recently admitted to hospital with a kidney infection, local media reported.
Born in Bizana in the Eastern Cape in 1936‚ Mandela moved to Johannesburg to study social work, gaining her degree in 1956.
The following year, aged 22, she was standing at a bus stop in Soweto when she was spotted by Nelson Mandela, who talked her into lunch the following week.
Mandela was married to Evelyn Mase, a devoted Jehovah's Witness and mother to four of his children. They divorced in 1958 and later that year Winnie and Nelson were married. They had two children together.
Five years later Nelson was arrested in 1963 and sentenced to life imprisonment for treason.
After she actively campaigned for his release she was banished to the town of Brandfort in the Orange Free State, where she was forced to remain, only allowed to leave to visit her husband at the prison on Robben Island.
In 1969 she was detained for 18 months in solitary confinement. But she would nonetheless continue campaigning.
After Nelson Mandela was released in 1990, the couple were famously pictured hand in hand walking from prison.
But just a year later, she was convicted of kidnapping and being an accessory to assault of Stompie Seipei‚ a 14-year-old activist who was killed by a member of her bodyguards‚ the Mandela United Football Club.
Together with Kenny Kgase, Pelo Mekgwe and Thabiso Mono, the teenager was taken from the home of Methodist minister Paul Verryn in 1989.
His body was recovered on waste ground near Winnie Mandela's house, his throat cut.
When Jerry Richardson was later convicted of the murder, he claimed she had ordered the kidnapping and attack, a claim she denied.
She was jailed for six years - a sentence that was reduced to a fine and a two-year suspended sentence on appeal.
In 1998, the country's Truth and Reconciliation Commission, chaired by Archbishop Desmond Tutu, condemned her for human rights violations after evidence from 30 witnesses.
"The Commission finds that Ms Madikizela Mandela was central to the establishment and formation of the Mandela United Football Club, which later developed into a private vigilante unit." its final report read.
"The Commission finds that those who opposed Ms. Madikizela-Mandela and the Mandela United Football Club, or dissented from them, were branded as informers and killed."
It went on to say that she was "accountable, politically and morally, for the gross violations of human rights committed by the Mandela United Football Club" and that she was personally "responsible for committing such gross violations of human rights."
Only an emotional plea from the archbishop led her to apologise.
None of this appeared to damage her political reputation.
After the county's first democratic election in 1994‚ Madikizela-Mandela become deputy minister of arts and culture, but she was later fired by her husband after making an unauthorised trip to Ghana.
After 37-years of marriage, the couple divorced in 1996.
She would go on to lead the ANC's Women's League and ran for deputy president, but resigned from all leadership positions after being found guilty in 2003 of fraud and theft in connection to a bank scam.
However, she remained an MP until her death and in 2016‚ she was bestowed with the Order of Luthuli in Silver, an award granted by the South African president, for her excellent contribution to the fight for the liberation of the nation's people.
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