SAO PAOLO, Brazil (TheStreet) -- Dilma Rousseff, a former leftist guerrilla, won Brazil's presidential election Sunday.

The hand-picked successor of the popular current president, Luiz Inacio Lula da Silva, Rousseff defeated centrist opponent Jose Serra decisively.

Brazil's electoral court said that with 99% of ballots counted, Rousseff had 55.6% of the vote, vs. 44.4% for Serra, the

Associated Press

reported.

"I'm very happy. I want to thank all Brazilians for this moment and I promise to honor the trust they have shown me," Rousseff said in her first public statement as president-elect, the

AP

reported.

At the beginning of October, Rousseff had won a first-round election with multiple candidates, but she failed to win the 50% of votes necessary to stave off another election.

Rousseff benefited from the popularity of her mentor, who enjoyed 80% approval ratings and campaigned aggressively for her. Brazil's constitution bars da Silva from serving a third term as president.

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This article was written by a staff member of TheStreet.