The election commission gave the Marxist People's Movement for the Liberation of Angola (MPLA) a 51.17% majority after all votes were counted while its longtime opponent, the National Union for the Total Independence of Angola, or UNITA, got 43.95%, its best result ever.
Official results announced by the National Electoral Commission (CNE) reported "The CNE proclaims Joao Manuel Goncalves Lourenco, president of the republic," commission head Manuel Pereira da Silva told a press conference.
Lourenco on Monday promised dialogue across sections of society after his party emerged victorious but with record low number of votes from a tight election.
"This vote was a vote of confidence, which gives us the immense responsibility of promoting dialogue and social consultation," he said in his inaugural address shortly after being declared winner of the August 24 vote.
The vote was the tightest in Angola's history.
UNITA leader Adalberto Costa Junior has rejected the results, citing discrepancies between the commission's count and the main opposition coalition's own tally.
Costa last week called for an international panel to review the count.
He did not immediately respond to the final results announcement.
The MPLA, a former liberation movement, has ruled Angola since independence from Portugal in 1975.
But it has seen a steady decline in support over recent elections.
Fewer than half of Angola's registered voters turned out for Wednesday's election, which despite being the closest fought yet, will extend the rule of MPLA to beyond 50 years since independence from Portugal in 1975.
Lourenco, a 68-year-old former general educated in the Soviet Union, was first elected in 2017, winning 61 percent of the vote.
This report was prepared with information from Agence France-Presse and Reuters