The election will determine whether Brazil remains one of South America's few left-wing countries or whether it will have a right-wing government under Bolsonaro, with close ties to US President Donald Trump.
The election looks set to be unusually close. In the first round, Bolsonaro took the lead with 47 percent of the vote to Lula's 45 percent. According to a new poll, the candidates are now tied at 50 percent each.
Incumbent President Lula met voters on Copacabana Beach in Rio de Janeiro on Saturday.
Bolsonaro, in turn, met voters at the house in Rio de Janeiro where his father, Jair Bolsonaro, recovered after being stabbed during the 2018 presidential campaign.