Early results showed the African National Congress with 64 percent, battering the hopes of the Congress of the People (COPE) party, formed by ANC dissidents, that it might pose the first real challenge since the end of apartheid in 1994.
Zuma portrays himself as a champion of the poor, and for many voters the ANC’s credentials from the fight against white minority rule still outweigh frustrations with its failure to tackle widespread crime, poverty and AIDS.
"We do not want to declare yet but this is an early indication of a decisive victory," ANC spokeswoman Jessie Duarte
COPE won nearly 8 percent of the early votes counted. The biggest challenge came from the Democratic Alliance — led by a white woman — with just under 19 percent.
Opposition parties hoped to at least deprive the ANC of the two-thirds parliamentary majority that lets it change the constitution and entrench its hold, but with a quarter of the vote counted it was unclear that would be the case.
"I think it could go either way for the ANC in terms of the two-thirds majority," said political analyst Adam Habib of the University of Johannesburg.
The final result is not expected before Friday but there is little doubt the 67-year-old Zuma will become president only three weeks after managing to get prosecutors to drop an eight-year-old corruption case that had tainted his reputation.
The rand firmed slightly early on Thursday after the smooth election, but later gave up the gains.
Among Zuma’s first tasks will be reassuring foreign investors who fear trade union allies will push him towards the left at a time the continent’s biggest economy could already be in recession for the first time in 17 years.
He has repeatedly said there will be no nasty surprises in store for investors and his room for policy manoeuvre is limited because of the global downturn. Finance Minister Trevor Manuel, a market favourite, is expected to stay for now.
Zuma has also pledged to tackle the rampant violent crime which could mar next year’s hosting of the soccer World Cup.
"I’m giving the ANC one last chance to deliver and I am hoping that they will deliver this time and if they don’t, things will have to change next time," said Herry Nkosi, 39, an accountant.
Election officials estimated the turnout in Wednesday’s vote at 76 percent — the same as 2004, when the ANC won 70 percent of the vote. Most analysts see that share slipping because of the new opposition challenge.
In an indication of at least a localised shift against the ANC, the Democratic Alliance for the first time defeated the ruling party on Robben Island, where Nelson Mandela, Zuma and other political prisoners were held during apartheid.
Police said the election was largely peaceful, although COPE said one of its officials was shot dead in what it believed to be a political killing.