In the late afternoon, most surveys closed in most countries. A long-lasting recession, heightened uncertainty and a massive corruption scandal that shook political and financial institutions were among the many issues that voters considered.
Polls closed in most major cities in the country, including the capital Brasilia, Sao Paulo and Rio de Janeiro.
Due to a time zone difference, the polls will be completed later on Sunday in the western state of Acre  Bolsonaro won the first round of elections this month in a field of 13 contestants. But he missed the 50% he needed to win over Haddad from the Labor Party.
"This was an unprecedented election," said Marco Antonio Teixeira, professor of political science at the Getulio Vargas Foundation. "The rhetoric used by both contestants during the campaign was extremely aggressive."
Politically Motivated Violence
This animosity has spread to the streets. Dozens of politically motivated acts of violence have been registered by voters, journalists and politicians.
Bolsonaro, 63, was stabbed in the stomach last month at a rally in the town of Juiz de Fora, in the state of Minas Gerais.
The incident took him weeks back from the campaign as he recovered. But it has strengthened its position among Brazilians looking for a change.
Others fear that the election could lead to more discrimination and hate crimes.
Bolsonaro's increased visibility led to a social media backlash known as #elenao or #nothim, which found support nationwide and internationally.
During his Brazil tour, Pink Floyd co-founder Roger Waters introduced the slogan on stage in neon lights and sang "ele nao" with the crowd.
Protesters have also sung the song during a recent "Women Against Bolsonaro march" in Sao Paulo.
"Bolsonaro has opened a Pandora box," said protest organizer Luka Franca. "He has given a voice to an ultra-right people who express their prejudices and want to destroy anyone who is different."
Bolsonaro, with US President Donald Trump and Philippine President Rodrigo Duterte, has sparked controversy over misogynist, racist and homophobic remarks.
He once told a congressman that she did not deserve to be raped because she was "very ugly," the Brazilian TV Globo reported.
He also said publicly that he would rather see his son die in an accident. to be homosexual as a member of his family.
"This negative discourse that it spreads kills people," said Felipe Lago, a 29-year-old fashion producer CNN. "If he wins, who knows what's going to happen to us?"
Lago has an Instagram account called "elenaovaoinosmatar "or" he will not kill us "created in English shortly after he was verbally attacked and threatened by a group of Bolsonaro supporters and threatened to be gay
" Although I was scared, I decided to post on Facebook what was mine happened, "said Lago. "I received many replies from friends and others who said that the same thing happened to them."
His Instagram account has more than 100,000 followers and contains videos of others claiming to have experienced similar attacks.
In Their Final Days During the election campaign, both Bolsonaro and Haddad called on their followers not to act too violently.
"Fake News" scandal
Laura Chinchilla, the head of the Organization of American States Mission of Observers for the Sunday elections, said she was worried about a fake news "phenomenon" during the Campaign seen
"The phenomenon we see in Brazil may be the first of its kind, mainly because it differs from other electoral campaigns in other countries," Chinchilla said on Thursday in Sao Paulo.
Most campaigns target Haddad's Labor Party, Folha de Sao Paulo reported.
According to the investigation by Folha de Sao Paulo, the tactic is considered illegal campaign financing.
Facebook has also shut down several groups and users accounts in Brazil this week after identifying them as "fake accounts," according to a statement by the Social Media Company.
"Authenticity is central to Facebook, so we ask if people are using their real name and why we are banning false accounts and other tactics that bad actors use to misrepresent their identity," the statement says.
As part of our ongoing effort to protect our community from this type of abuse, Facebook has removed 68 pages and 43 accounts from a Brazilian marketing group, Raposo Fernandes Associados (RFA), for violating our misrepresentation and spam policies ,
The RFA group had established several pro-Bolsonaro sites and groups, including media organizations, magazines, political groups and television stations.
Bolsonaro's supporters believe that the Whatsapp and Facebook scandals were created by Haddad's Labor Party (PT) as a distraction because they lag behind in the polls. They also accused Folha de Sao Paulo of being biased and threatening journalists involved in the investigations.
"There is no evidence," said Fabio Silveira, an engineer, during a recent Pro Bolsonaro event. "This is one of the PT's strategies, and they have reached a point where they realize that they can not win and now try to destroy the image of the opposition candidate with false stories."
Leaving the workers' party outside
For some Brazilians, like teacher Alexandre Vastella, choosing Bolsonaro is more for supporting the Labor Party (PT) to leave office.
"I want Bolsonaro to be president, not because he's the ideal person, but because we can not risk bringing the PT back to power," Vastella told CNN. "Sure, all the major parties are corrupt, but the PT has created a corrupt infrastructure."
The Labor Party ruled Brazil for more than 13 years under President Luiz Inacio Lula da Silva from 2003 to 2011 and his successor Dilma Rousseff, from 2011 to 2016.
Lula, as he is popularly known, left office 83% approval after its policies helped lift millions of Brazilians out of poverty.
Many politicians, including Lula, were arrested in an extensive four-year anti- Graft probe called "Operation Car Wash." He was arrested in April and sentenced to 12 years for corruption and money laundering.
Despite the arrest, Lula ran for a third term and led the elections until he was expelled from the country's Supreme Electoral Tribunal in September. His colleague Haddad replaced him in the vote and became the standard candidate of his party.
The election is compulsory in Brazil, ie everyone has to vote on election day. Some undecided voters, such as Sao Paulo-based Mauricio Soares, choose to vote zero or empty.
"The decision to vote zero came after many considerations and I am firm in my decision," Soares told CNN. "I am not neutral, I am positioning myself against both candidates."
Professor Teixeira said the winner must bridge the gap created by the campaign.
"If the next president rules only for his followers, the division we live will remain, and if he decides to rule for the entire country, there is a greater chance that those conflicts will be minimized or disappeared," Teixeira said ,