Tambo was one of the founder members of the ANC Youth League (ANCYL) in 1944 with Nelson Mandela and Walter Sisulu, and was elected as the organisation's Secretary. He was appointed as the Secretary General of the ANC in 1954.
With the banning of the ANC and other liberation movements in 1961 Tambo was given the mandate to establish ANC mission offices in exile. He started both the UK/Ireland and Lusaka Missions and was at the fore of mobilisation of the armed struggle and guerrilla campaigns against apartheid.
When ANC President Chief Albert Luthuli died in 1967 Tambo was appointed as Acting President. He was elected as President of the organisation during the Morogoro Conference in 1969. Oliver Tambo passed away on 24 April 1993.