He was one of the founders of the ANC Youth League in 1944 and its first National Secretary. In 1948 he was elected onto the National Executive of the ANC.
In 1955 he became Secretary General of the ANC after Walter Sisulu was banned by the South African government under the Suppression of Communism Act. In 1958 he became Deputy President of the ANC and in 1959 was served with a five year banning order by the government.
In 1960 the ANC sent him abroad in order to mobilise opposition to apartheid. He was involved in the formation of the South African United Front which achieved the expulsion of South Africa from the Commonwealth in 1961.
In 1985 he was re-elected President of the ANC. He returned to South Africa in 1991 after over 30 years in exile. He was elected National Chairperson of the ANC in July 1991.
He first had a stroke in 1989. It was another stroke that killed him in 1993.