Jacob Zuma has defeated South African President Thabo Mbeki to win leadership of the ruling African National Congress (ANC).
The former ANC deputy-leader was widely expected to oust South African President Thabo Mbeki as party chief in the vote, which was delayed by two days of wrangling between supporters of the two rivals at a party congress.
Mr Zuma is now almost certain to become president when Mr Mbeki stands down in 2009.
Mr Zuma received 2,329 votes, ahead of Mr Mbeki's 1,505 votes. Chaos erupted in the hall as the results were announced, then Mr Mbeki and Mr Zuma mounted the stage together and embraced.
The 3,900 delegates also voted for five other ANC leadership positions.
Mr Zuma, whom Mr Mbeki sacked from government over bribery allegations two years ago, has since successfully fought off separate corruption and rape charges. However, he faces arrest in the coming months as part of a state-sponsored fraud investigation.
Mr Zuma has said that, if elected party leader, he would not step down if he was charged with corruption.
Backed by trade unions, Mr Zuma went into the congress with huge momentum over Mbeki, who has become increasingly unpopular with the rank and file, who say he is autocratic and has moved too slowly to help millions of poor blacks. President Mbeki took control of the party from Nelson Mandela in 1997, succeeding him as head of state in 1999. Markets fear Zuma could reverse Mbeki's centrist policies, which have fuelled the longest period of growth in Africa's economic powerhouse. There are also concerns of a long period of uncertainty over the next 18 months until the 2009 election, with the presidency and party leadership split between the two men and Zuma facing possible charges.
This has generated heightened fears within certain sections of the party that he will damage the reputation of the ANC, if not South Africa.
Mr Zuma has tried to reassure investors there would be no sweeping economic policy changes under his leadership.
He has called for Aids and crime to be declared "national emergencies", and has also signalled he will take a stronger stance on Zimbabwe than Mr Mbeki.