Ahmed Kathrada poses next to his close friend, Mandela's photo
Mr Kathrada, often referred to as Kathy, passed away peacefully in Johannesburg’s Donald Gordan Hospital, in the early hours of Tuesday morning.
The Ahmed Kathrada Foundation said the veteran activist’s death followed “a short period of illness, following surgery to the brain”.
Alongside Nelson Mandela, Mr Kathrada was among eight African National Congress activists who were sentenced to life imprisonment in 1964.
They were convicted of trying to overthrow the apartheid government.
Upon his release in 1989, President Mandela persuaded him to join his government.
Kathrada, right, was a close friend of Mandela's until his death
Mr Kathrada supported the former South African president until 1999, but remained politically active.
Neeshan Balton, the director of the Ahmed Kathrada Foundation said: “This is great loss to the African National Congress, the broader liberation movement and South Africa as a whole.
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“Internationally, he was staunch in his support for the Palestinian struggle. Kathy was an inspiration to millions in different parts of the world.”
His fellow Robben Island prisoner, Laloo “Isu” Chiba said Kathrada’s death had left a deep vacuum in his life.
Kathrada and Mandela were imprisoned together for campaigning against the apartheid
Kathrada making Mandela laugh before the former President's historic parliament speech
Mr Chiba added: “I have worked with ‘Kathy’ for over 60 years. He has been my strength in prison, my guide in political life and my pillar of strength in the most difficult moments of my life. Now he is gone.”
Mr Kathrada will be buried according to Muslim religious rites. Details of the burial will be made public in due course.