Brasília, Brazil - In a stunning comeback, left-wing challenger and former president Luiz Inácio Lula da Silva has won the Brazilian presidential runoff against far-right incumbent Jair Bolsonaro, the electoral commission said on Sunday evening.

Lula got 50.83% of the votes in the runoff, the electoral office in Brasília said. Bolsonaro received 49.17% of the votes.

"At 7:56 PM [8:56 PM EDT] this Sunday (10/30), the candidate Lula (PT) is mathematically elected to the presidency of the Republic with 50.83% of the votes. Jair Bolsonaro (PL) had 49.17%," the electoral commission tweeted.

A former trade union official, Lula ruled the largest country in Latin America from early 2003 to late 2010.

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"On this historic 30th of October, the majority of the Brazilian people made it very clear that they want more – not less democracy," Lula tweeted following the electoral commission announcement.

"As of January 1, 2023, I will govern for 215 million Brazilians, not just those who voted for me. There are not two Brazils. We are a single country, a single people, a great nation," Lula added.

The 77-year-old is Brazil's first democratically elected president to serve a third term.

In addition to the head of state, governors were also elected in a dozen states on Sunday.

US President Joe Biden sent his congratulations to Lula after the result was declared.

"I send my congratulations to Luiz Inácio Lula da Silva on his election to be the next president of Brazil following free, fair, and credible elections. I look forward to working together to continue the cooperation between our two countries in the months and years ahead," Biden said in a statement.

The atmosphere in Brazil was very tense in the run-up to Sunday's runoff in view of major differences between the two political camps and their contrasting visions for the country.

The already intense election campaign became increasingly dirty in the countdown to the vote.

Brazilians have been bombarded with a flood of misinformation, especially on social media and via WhatsApp groups.

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Many of his followers associate Lula with Brazil's golden age, when the economy boomed due to high commodity prices and the government lifted millions of people out of abject poverty with the help of social programs.

But there were fears that violence could break out after a Lula election victory. Firearms laws have been relaxed during the tenure of Bolsonaro, a former military man, and many of his supporters have heavily armed themselves.

Some of his supporters had also unashamedly called for a military coup.

Lula had won the first round of the presidential election on October 2, but by a much narrower margin than predicted by opinion polls, after which the race was considered completely open again.

This particular Brazilian election also had potential international ramifications. As a huge carbon reservoir, the Amazon region plays an important role in the fight against global climate change.

Large-scale deforestation of the Amazon region accelerated under Bolsonaro, with his government trashing environmental laws and pushing to open Indigenous lands to commercial exploitation. Lula is expected to take a pro-environment stance as president.

In addition, Brazil is a potentially important trading partner with its enormous natural resources, high proportion of green energy, and large agricultural economy.