Nearly 150 million people are eligible to vote in the election today.
But if no candidate gets more than 50 percent of the ballots, there will be another chance to vote in three weeks.
No candidate seems likely to get this majority, so a runoff vote has already been scheduled for October 28.
The front runner is far-right populist candidate and former paratrooper Jair Bolsonaro, who is pro-torture.
He wants to tackle crime and record-high murder rates, as 63,880 people were killed last year.
His competition is the left-wing candidate for the Workers’ Party, Fernando Haddad.
He is a former mayor or Sao Paulo and replaced former President Luiz Ignacio Lul da Silva, who was dropped as a candidate after he was jailed for corruption.
Other candidates include the centrist trio Ciro Gomes, Geraldo Alckmin and Marina Silva.
They are aiming to patch up a deeply divided country, however, they are unlikely to win.
Brazilians will also vote for 27 governors and nearly 1,600 lawmakers on Sunday too.
When do polls close?
People will be able to cast their ballot between 8am and 5pm local time.
Voting is compulsory in Brazil for all people who are 18 to 70 years old.
If anyone fails to vote without any justification may be fined and could counter problems when renewing passports or IDs.
What time will we have a result?
The results are expected late Sunday.