It was launched on December 16, the same day as the Afrikaners defeated the Zulus at the Battle of the Blood River 100 years earlier, not long after the massacre in Sharpeville of 69 unarmed protesters by the security police.
Mr Mandela was adamant that MK, as the armed unit was called, would not kill people but its tactics would be aimed at sabotage. In his own words, the aim was to "hit back by all means within our power in defence of our people, our future and our freedom".
On his return to South Africa, Mr Mandela and his colleagues set up regional command units and set about training their army in bomb making and clandestine operations.
MK carried out numerous bombings during the next 20 years and the pledge not to kill became redundant – in the whole campaign, at least 63 people died and 483 people were injured.
It was subsequently classified as a terrorist organisation by the South African government and the United States, and banned.
The armed struggle would also have a very personal consequence for Mr Mandela: he was arrested for sabotage a year after MK's formation, and would spend the next 27 years in prison.
Operations continued in his absence and among MK commanders was Jacob Zuma, now the South African president, but were suspended in August 1990 in preparation for the dismantling of apartheid and the birth of the Rainbow Nation.