After the 1948 election victory of the Afrikaner-dominated National Party, which supported the apartheid policy of racial segregation,Mandela began actively participating in politics. He led prominently in the ANC's 1952 Defiance Campaign and the 1955 Congress of the People, whose adoption of the Freedom Charter provided the fundamental basis of the anti-apartheid cause.
In 1961 Mandela became leader of the ANC's armed wing, Umkhonto we Sizwe (translated Spear of the Nation, and also abbreviated MK), which he co-founded.He coordinated sabotage campaigns against military and government targets, making plans for a possible guerrilla war if the sabotage failed to end apartheid. Mandela also raised funds for MK abroad and arranged for paramilitary training of the group.
On 5 August 1962 Mandela was arrested after living on the run for seventeen months, and was imprisoned in the Johannesburg Fort.A large number of groups have been accused of tipping off the police about Mandela’s whereabouts including the South
African Communist Party, Mandela’s host in Durban GR Naidoo, and the CIA, but Mandela himself considers none of these connections to be credible and instead attributes his arrest to his own carelessness in concealing his movements.Of the CIA link in particular, Mandela's official biographer Anthony Sampson believes that "the claim cannot be substantiated."
Three days later, the charges of leading workers to strike in 1961 and leaving the country illegally were read to him during a court appearance. On 25 October 1962, Mandela was sentenced to five years in prison.
Mandela was imprisoned on Robben Island where he remained for the next eighteen of his twenty-seven years in prison. While in jail, his reputation grew and he became widely known as the most significant black leader in South Africa. In 1988 Mandela was moved to Victor Verster Prison and would remain there until his release.
On 2 February 1990, State President F. W. de Klerk reversed the ban on the ANC and other anti-apartheid organisations, and announced that Mandela would shortly be released from prison. Mandela was released from Victor Verster Prison in Paarl on 11 February 1990. The event was broadcast live all over the world.
South Africa's first multi-racial elections in which full enfranchisement was granted were held on 27 April 1994. The ANC won 62% of the votes in the election, and Mandela, as leader of the ANC, was inaugurated on 10 May 1994 as the country's first black President.
Mandela became the oldest elected President of South Africa when he took office at the age of 75 in 1994. He decided not to stand for a second term and retired in 1999, to be succeeded by Thabo Mbeki.