|Al Jazeera's Gabriel Elizondo reports from the capital Brasilia, where Rousseff supporters have been celebrating.
Dilma Rousseff has won Brazil's presidential election and will become the first woman to lead the Latin American economic powerhouse.
Rousseff was declared winner of Sunday's poll by more than 10 percentage points, beating rival Jose Serra with 55.5 per cent of valid votes cast to his 44.5 per cent.
The 62-year-old former guerrilla leader will be sworn in as the country's president on January 1 after running a campaign that highlighted her links to outgoing president Luiz Inacio Lula da Silva.
In her first pledge as president-elect, Rousseff vowed to eradicate poverty affecting 20 million people in her nation.
"I reiterate my fundamental promise: the eradication of poverty," the leftwinger said in her victory speech in Brasilia. "We must not rest while there are Brazilians going hungry."
"Eradicating extreme poverty is my goal. But I humbly ask for the support of all who can help the country bridge the gap dividing us and make us a developed nation."
Silva used his 80 per cent approval ratings to campaign for Rousseff, his former chief of staff and political protege.
Rousseff will take power in a nation on rise, a country that will host the 2014 World Cup and that is expected to be the globe's fifth-largest economy by the time it hosts the 2016 Summer Olympics.
"Her government will focus primarily on solving Brazil's bottlenecks," Fernando Pimentel, a close adviser to her campaign, said in a recent interview.
Rousseff has never held elected office and lacks the charisma that transformed Silva from a one-time shoeshine boy into one of the globe's most popular leaders.
In the 1960s she fought against the military dictatorship ruling Brazil in the 1960s, spending time in prison before studying economics and making a name for herself as a competent technocrat.
She held a range of mid-level government posts before Silva made her his energy minister, chief of staff, and then named her as his political successor.
Silva has served two four-year terms and is barred by Brazil's constitution from running for a third. He has batted down chatter in Brazil's press that he is setting himself up for a new run at the presidency in 2014, which would be legally allowed.
That does not mean many voters do not want him to stay. "If Lula ran for president 10 times, I would vote for him 10 times," Marisa Santos, a 43-year-old selling her homemade jewelry on a Sao Paulo street said.
Rousseff's victory was not as straightforward as many predicted.
In the first round of the presidential election on October 3, Rousseff got 46.9 per cent of the votes, falling just short of the majority needed to avoid a runoff. Serra finished second with 32.6 per cent.
Marina Silva, a former environment minister and no relation to the president, took 20 million votes, leaving Rousseff and Serra to scramble for her supporters during the second round
About 135 million voters were obliged to cast ballots on Sunday. Under Brazilian law, voting is mandatory for citizens between the ages of 18 and 70.