Meanwhile, in his concession speech, Haddad pledged to continue to fight for "national sovereignty and democracy" in Brazil, saying that Bolsonaro's win jeopardized basic freedoms.

"What is at stake are civil, labor and social rights. We have the huge task of defending them," said Haddad.

With some 21 percent abstention, nearly 10 percent of the votes were either left blank or nullified, according to the TSE.

"Perhaps never before" has it been so necessary for the Brazilians to exercise their rights as citizens to defend democratic institutions, said Haddad.

Following the release of the official results, Brazilian President Michel Temer congratulated Bolsonaro in a telephone call, saying that Bolsonaro's government would be marked by "peace and harmony."

"I firmly believe, as the president-elect was able to declare, that he will make a government of much peace and harmony, which is what our country most needs," said Temer.

"He very much thanked the phone call and said he will continue to work towards pacification," Temer told reporters at his residence.

The transition of power will begin on Monday at the cultural center of the Bank of Brazil, which is close to the presidential headquarters in Brasilia, said Temer.