Sonia Bunting, the indomitable SA Communist Party activist famed for organising an international campaign that helped save Nelson Mandela and others from the death penalty, died after a short illness on Saturday at the age of 78.

In decades of dedicated work for the Communist Party Bunting is probably best known for her organisation, from exile in London, of the World Campaign for the Release of South African Political Prisoners - the movement that mobilised international support for the Rivonia trialists and led to the stepping-up of economic boycotts against South Africa.

She was one of the 156 activists charged with high treason in 1956 in the lead-up to the Rivonia treason trial.

Although acquitted two years later, she was subsequently banned, detained again for 3½ months at Pretoria Central prison in 1960, and placed under house arrest in 1962.

"Sonia believed socialism was the only answer to the problems of the world," said her husband, Brian, on Sunday.

"She was motivated by the desire to put an end to inequalities between races and classes by making the fruits of the world available to everybody. She stuck to her ideals throughout her life.

"She was a source of continual ideas. Her most striking qualities were straightforwardness, integrity, determination and simplicity."

Bunting said the arrests did little to quell her spirit - if anything, they consolidated her resolve.

Bunting completed her first year of medical studies at the University of the Witwatersrand, but left to work for the Communist Party.

"It was the atmosphere of the times, coming to the end of the World War 2 and, with it, the end of fascism that changed the world," said her husband. "Sonia and her friends decided they could do the same for Africa."

After the Suppression of Communism Act of 1950 Bunting worked for the banned publication, Guardian, which changed its name to Spark and New Age until 1963 when all its writers, including Govan Mbeki and Ruth First, were banned and the publication folded.

She was also a platform speaker at the Congress of the People in Kliptown in 1955 where the Freedom Charter was adopted.

Six months after she and her husband were placed under house arrest in 1962, the couple went into exile in London with their children.

Bunting is survived by her husband of 55 years, Brian, and their children Peter, Margaret and Stephen. A memorial meeting is expected to be held at Maitland cemetery on Saturday at 11am, although details are still to be confirmed.