Former Cape Town Archbishop Desmond Tutu says he will no longer vote for the governing African National Congress party.
In an article in The Mail & Guardian newspaper, the Nobel laureate said the ANC is good at leading the struggle against oppression, but has not made the transition to becoming a political party.
He cited inequality, violence, and corruption as among the reasons for his withdrawal of support.
Archbishop Tutu, 81, was also strongly critical of past decisions made by the ANC government at the UN, particularly on Zimbabwe.
"The things we have voted for or against have been a disgrace. It has been a total betrayal of our whole tradition."
Archbishop Tutu campaigned against white minority rule and was awarded the 1984 Nobel Peace Prize.
But the BBC reports he has been increasingly critical of the ruling party in recent years.
In 2011, he accused the ANC government of "kowtowing" to China, after the government delayed issuing a visa for the Dalai Lama, who had been invited to attend the archbishop's 80th birthday celebrations.
In the opinion piece, he also warned South Africa to prepare for Nelson Mandela's death.
"My concern is that we are not preparing ourselves, as a nation, for the time when the inevitable happens."
"He's 94, he's had a rough time, and God has been very, very good in sparing him for us these many years.
''But the trauma of his passing is going to be very much intensified if we do not begin to prepare ourselves for the fact that this is going to happen at some time," he added.