POLOKWANE, South Africa — The populist Jacob Zuma swept to power last night as the leader of South Africa’s ruling African National Congress.

His victory over the incumbent, Thabo Mbeki, capped a stunning comeback two years after Mr. Mbeki sacked him as national deputy president when Mr. Zuma’s financial adviser was convicted of fraud.

It was the ANC’s first publicly contested leadership election in more than half a century and 13 years after the end of apartheid. Before the result was announced at the ANC’s national conference in Polokwane, rival supporters chanted: “Thabo Mbeki, my president” and “Zuma is mine.”

First Mr. Mbeki’s 1,505 votes were announced, then Mr. Zuma’s 2,329 — but before the returning officer had completed the word “thousand” the marquee erupted into cheers, whistles, drumbeats, and chants of “Zuma, Zuma.”

In a gesture of reconciliation after a bruising battle, the two men took the stage together and embraced.

For the final 18 months of his term as national president, Mr. Mbeki will have to face a competing center of power in the ANC as Mr. Zuma tries to assert his authority.

Foreign investors in South Africa will be watching closely for signs of Mr. Zuma’s policies given that his new position makes him favorite to become the country’s next president.

The leadership campaign was marked by acrimony and disputes, and Mr. Mbeki was humiliated when, as the gathering opened on Sunday, Mr. Zuma’s supporters sang the challenger’s campaign song “Bring Me My Machine Gun” at him.

“I think democracy has prevailed,” Andries Magongoa from Limpopo said last night. “I think the members of the ANC have spoken. In the ANC, if the majority take a decision, the minority should have to accept the result.” But wounds will take a long time to heal, and the battle for power in South Africa is far from over.

Mr. Zuma could not be a more contentious figure. He was acquitted of raping an HIV-positive woman last year and is facing investigations for corruption and tax evasion. A conviction in either would leave him ineligible to become head of state.

He insists that the allegations are politically motivated, but those opposed to him will redouble their efforts to bring him to trial before the next general election in 2009.

Mr. Zuma has repeatedly portrayed himself as an ANC loyalist, saying he will adopt a consensus leadership style, in contrast to the aloof Mr. Mbeki.

But a Zuma presidency would undoubtedly see change in South Africa. He is seen as “pro-poor” and has strong backing from trade unions and the South African Communist Party, which wants to see increased social spending.

“When he was chased out of the Parliament, he went to the rural areas and saw how people are suffering,” Mlungisi Ngcobo, from Mr. Zuma’s home province of KwaZulu-Natal, said. “We’re confident Zuma will come down and fulfill our needs.”

He has called for AIDS and crime to be “treated as national emergencies” — issues which Mr. Mbeki has been criticized over.