Joe Slovo was born in a small Lithuanian village, Obelai, on 23 May 1926, to parents Woolf and Ann. When Slovo was nine years old the family moved to Johannesburg in South Africa, primarily to escape the increasing threat of anti-Semitism which gripped the Baltic States. He attended various schools until 1940, including the Jewish Government School, when he achieved Standard 6 (equivalent to American grade 8).

Slovo first encountered socialism in South Africa through his school-leaving job as a clerk for a pharmaceutical wholesaler. He joined the National Union of Distributive Workers and had soon worked his way up to the position of shop steward, where he was responsible for organising at least one mass action. He joined the Communist Party of South Africa in 1942 and served on its central committee from 1953 (the same year its name was changed to the South African Communist Party, SACP). Avidly watching the news of the Allied front (especially the way in which Britain was working with Russia) against Hitler, Slovo volunteered for active duty, and served with South African forces in Egypt and Italy.

In 1946 Slovo enrolled at the University of Witwatersrand to study law, graduating in 1950 with a Bachelor of Law, LLB. During his time as a student Slovo became more active in politics, and met his first wife, Ruth First, the daughter of the Communist Party of South Africa's treasurer, Julius First. Joe and Ruth were married in 1949. After college Slovo worked towards becoming an advocate and defence lawyer.

In 1950 both Slovo and Ruth First were banned under the Suppression of Communism Act – they were 'banned' from attending public meetings and could not be quoted in the press. They both, however, continued to work for the Communist Party and various anti-Apartheid groups.

As a founder member of the Congress of Democrats (formed in 1953) Slovo went on to serve on the national consultative committee of Congress Alliance and helped draft the Freedom Charter. As a result Slovo, along with 155 others, was arrested and charged with high treason.

Slovo was released with a number of others only two months after the start of the Treason Trial. The charges against him were officially dropped in 1958. He was arrested and detained for six months during the State of Emergency which followed the 1960 Sharpeville massacre, and later represented Nelson Mandela on charges of incitement. The following year Slovo was one of the founders of Umkhonto weSizwe, MK (Spear of the Nation) the armed wing of the ANC.

In 1963, just before the Rivonia arrests, on instructions from the SAPC and ANC, Slovo fled South Africa. He spent twenty-seven years in exile in London, Maputo (Mozambique), Lusaka (Zambia), and various camps in Angola. In 1966 Slovo attended the London School of Economics and gained his Master of Law, LLM.

In 1969 Slovo was appointed to the ANC's revolutionary council (a position he held until 1983, when it was dissolved). He helped draft strategy documents and was considered the ANC's main theoretician. In 1977 Slovo moved to Maputo, Mozambique, where he created a new ANC headquarters and from where he masterminded a large number of MK operations in South Africa. Whilst there Slovo recruited a young couple, Helena Dolny, an agricultural economist, and her husband Ed Wechsli, who had been working in Mozambique since 1976. They were encouraged to travel into South Africa to undertake 'mappings' or reconnaissance trips.

In 1982 Ruth First was killed by a parcel-bomb. Slovo was accused in the press of complicity in his wife death – an allegation which was eventually proved unfounded and Slovo was awarded damages. In 1984 Slovo married Helena Dolny – her marriage to Ed Wechsli had ended. (Helena was in the same building when Ruth First was killed by a parcel bomb). That same year Slovo was asked by the Mozambican government to leave the country, in accordance with its signing of the Nkomati Accord with South Africa. In Lusaka, Zambia, in 1985 Joe Slovo became first white member of the ANC national executive council, he was appointed general-secretary of South African Communist Party in 1986, and chief-of-staff of the MK in 1987.

Following the remarkable announcement by President FW de Klerk, in February 1990, of the un-banning of the ANC and SACP, Joe Slovo returned to South Africa. He was a key negotiator between various anti-Apartheid groups and the ruling National Party, and was personally responsible for a 'sunset clause' which led to the power sharing Government of National Unity, GNU.

Following a bout of ill health in 1991 he stepped down as general-secretary of SACP, only elected as SAPC chairperson in December 1991 (Chris Hani replaced him as general-secretary).

In South Africa's first multi-racial elections in April 1994, Joe Slovo gained a seat through the ANC. He was awarded with the post of Minister for Housing in the GNU, a position he served under until his death form Leukaemia on 6 January 1995. At his funeral nine days later, President Nelson Mandela gave a public eulogy praising Joe Slovo for all he had achieved in the struggle for democracy in South Africa.

Ruth First and Joe Slovo had three daughters: Shawn, Gillian and Robyn. Shawn's written account of her childhood, A World Apart, has been produced as a film.