Jair Bolsonaro, known as 'Tropical Trump', is Brazil's new President

Bolsonaro's victory reflected widespread anger at the political class after years of corruption, an economy that has struggled to recover after a punishing recession and a surge in violence.

"I feel in my heart that things will change," hoped Sandra Coccato, a 68-year-old small business owner, who voted for Bolsonaro in Sao Paulo.

"There's a light at the end of the tunnel," she added.

In Sao Paulo, Brazil's largest city, car horns could be heard honking and crowds celebrated as the results came in.

There were also reports of clashes between his backers and opponents.

In Rio de Janeiro, thousands of supporters of Bolsonaro, who had cast himself as a political outsider despite a 27-year career in Congress, gathered on iconic Copacabana Beach, to celebrate the win.

Bolsonaro, who ran on promises to clean up Brazil and bring back "traditional values," said he would respect the Constitution and personal liberty.

"That is a promise, not the vain word of a man. It's a promise to God," he emphasized.

"I was never alone. I always felt the presence of God and the force of the Brazilian people," Bolsonaro said for his supporters.

Brazil's top electoral-court said Bolsonaro won with just over 55% of the vote, compared with just under 45% for rival Fernando Haddad of Workers' Party.

Bolsonaro was on Sunday the clear front-runner after getting 46% of the vote to Haddad's 29% in the first round of voting on Oct 7.

Opinion polls had him leading by 18 percentage points, but the race tightened thereafter.

Meanwhile, addressing supporters in Sao Paulo, Haddad delivered a speech promising resistance.

Interestingly, he didn't concede or even mention Bolsonaro by name in his discourse.

"We have the responsibility to mount an opposition, putting national interests, the interests of the entire Brazilian people, above everything," said the 55-year-old, adding, "Brazil has never needed the exercise of citizenship more than right now."

Experts suggest Bolsonaro's rise was powered by disgust with the political system.

In particular, many Brazilians were furious with the Workers' Party for its role in the mammoth graft scheme uncovered by the "Operation Car Wash" investigation.

Since then, Haddad has been struggling to build momentum with his promise to return the boom times by investing in health, education, and by reducing poverty.

On Sunday morning, Haddad was still holding out hope that he could win after receiving several key endorsements late Saturday.

Among them was a popular former Supreme Court justice, Joaquim Barbosa, who tweeted support for Haddad, saying Bolsonaro's candidacy scared him.

Likewise, former Attorney General Rodrigo Janot, one of the biggest crusaders against corruption in the Workers' Party in recent years, also endorsed Haddad.

Coming back to Bolsonaro, his candidacy had raised serious concerns that he would roll back civil rights and weaken institutions in what remains a young democracy.

He frequently disparaged women, gays, and blacks, and said he would name military men to his Cabinet.

Minutes after he was elected, several international human rights groups put out statements demanding that Bolsonaro respect Brazil's democracy.

On Sunday, the Chief Justice of the Supreme Court, Jose Dias Toffoli, read out part of the Constitution to reporters after he voted.

"The future President must respect institutions, must respect democracy, the rule of law, the judiciary branch, the national Congress and the legislative branch," Toffoli said in remarks many took to be a rebuke of Bolsonaro and his more extreme positions.

The past few years in Brazil have been exceptionally turbulent.

In 2016, the then President, Dilma Rousseff of the Workers' Party, who had held the position since 2011, was impeached and removed from office on charges, that many on the left felt were politically motivated.

Brazil's economy suffered a two-year recession and is now only beginning to emerge, with growth stagnant and unemployment high.