It is widely assumed that international pressure influenced the decision not to sentence Mandela and other convicted Rivonia defendants to death.
This page highlights some of the evidence for that assumption.
1. October 11, 1963: The United Nations General Assembly voted 106 to 1 (with only South Africa dissenting) to condemn apartheid repression and call upon South Africa "to abandon the arbitrary trial now in progress and forthwith to grant unconditional release to all political prisoners and to all persons imprisoned, interned or subjected to other restrictions for having opposed apartheid."
2. June 9, 1964 (two days before the Rivonia trial verdict), the U. N. Security Council adopted Resolution 190 on a vote of 7 to 0 (with four abstentions, including Great Britain, the United States, France, and Brazil). The resolution urged South Africa to end the trial and grant amnesty to all defendants.
3. U. N. representatives of 56 nations issued an appeal to all countries maintaining diplomatic relations with South Africa "to take all necessary measures to prevent the execution of African nationalist leaders now on trial in Pretoria."
4. Two nations with significant influence, the United States and Great Britain, made efforts to convince South Africa to not execute the Rivonia defendants. The exact nature of these steps is not known. Adlai Stevenson, the U.N. representative of the United States, promised in a letter that the U.S. would do everything within its power to prevent death sentences. Contacts with officials of the South African government convinced the British foreign service office in Capetown as early as May that death sentences were unlikely. A May report from Capetown to London indicated that the head of the South African Security Police did not expect executions and that prosecutor Percy Yutar would not ask for death sentences in his closing statement at the trial. (Yutar, in fact, did not request imposition of the death penalty.)
5. On the night before the verdict, British Consul General Leslie Minford assured defense attorney George Bizos that none of the accused would be sentenced to death. When Bizos asked Minford how he knew, he said the judge told him so.