Former academic Mike du Toit was convicted of treason last year for his role in the plot against the former president of South Africa after a nine-year trial.
Twenty other members of du Toit's white supremacist militia, the Boeremag, were convicted to spend anywhere from 5 to 35 years in jail.
In 2002 du Toit attempted to overthrow the ruling African National Congress. Witnesses testified that the Boeremag planned to assassinate Mandela by planting a bomb on a route the then-president was supposed to travel on. His plans were thwarted, however, when Mandela traveled to his engagement by helicopter.
Boeremag members were charged with causing nine explosions at different sites on October of 2002. Nine of the accused members were allowed to walk free after the trial given the 11 years they had already spend behind bars.
Du Toit was the first person to be convicted of treason in South Africa since white minority rule ended in 1994. During the trial he was also found guilty of starting a conspiracy that intended to evict black South Africans from most of the country in order to establish a "pure" nation.