"I send my congratulations to Luiz Inacio Lula da Silva on his election to be the next president of Brazil following free, fair, and credible elections," Biden said in a statement.
Adding to tensions in Brazil, Bolsonaro has made baseless attacks on the integrity of Brazil's electronic voting system and suggested he may not concede if he loses.
Brazil's most polarised election in decades will decide whether to return to power the leftist leader who spent time in jail on corruption convictions or the right-wing populist who has attacked the voting system and threatened to contest defeat.