The ANC took 69.68% of vote, according to final figures released by the Independent Electoral Commission on Saturday.
The party improved its standing in all nine of the country's provinces.
The main opposition Democratic Alliance, led by Tony Leon, a tough-talking white, was way behind with 12.37% of the ballot and short of the 17% he had earlier promised.
The Zulu-based Inkatha Freedom Party was in third place with 6.97%.
The main loser was the New National Party, a reincarnation of the party which formed the backbone of apartheid South Africa, which got only 1.65% of the vote.
Promises for second term
Mbeki told jubilant supporters feting the former liberation movement's third straight - and biggest - that he would stand by his pledge to ensure "a better life for all."
Poverty is still an acute problem and unemployment hovers between 40 and 50%.
Exacerbating this is the fact that South Africa has the highest HIV/AIDS caseload in the world.
Taking the victory salute, Mbeki said the electorate were "renewing the mandate of the ANC so that we do even better than we have done in the past to serve the people of South Africa.
Over three quarters of the
electorate turned out to vote
The president had promised in his election campaign to create one million new jobs in five years; pledged 100 billion rand ($15 billion) to improve infrastructure and vowed to halve poverty and unemployment by 2014.
The electoral commission said turnout for Wednesday's vote at 76.73% was much lower than the previous two democratic elections of 1994 and 1999.
South Africa's 400-seat assembly will convene next week to elect the new president, who is almost certain to be Mbeki.
The presidential inauguration is scheduled for 27 April as the country holds festivities marking the 10th anniversary of the end of apartheid with foreign dignitaries invited to attend.