With nearly 95 percent of the ballots counted, Rousseff had 55.6 percent compared to 44.4 percent for her centrist rival, Jose Serra, the electoral court said. Rousseff, the hand-chosen candidate of wildly popular President Luiz Inacio Lula da Silva, won by cementing her image to Silva's, whose policies she promised to continue.
She will lead a nation on the 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. It has also recently discovered huge oil reserves off its coast.
Rousseff was already speaking like a president-elect when she cast her vote Sunday morning. "Starting tomorrow we begin a new stage of democracy," Rousseff, 62, said in the southern city of Porto Alegre, where she cast her vote. "I will rule for everyone, speak with all Brazilians, without exception."
Silva used his 80 percent approval ratings to campaign incessantly for Rousseff, his former chief of staff and political protege. She never has 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.
Silva was barred by the constitution from running for a third consecutive four-year term. 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 legal.
Despite Rousseff's win, many voters don't want "Lula," as he is popularly known, to go away.
"If Lula ran for president 10 times, I would vote for him 10 times," said Marisa Santos, a 43-year-old selling her homemade jewelry on a Sao Paulo street. "I'm voting for Dilma, of course, but the truth is it will still be Lula who will lead us."
Silva entered office with a background as a leftist labor leader, but he governed from a moderate perspective. Under his leadership, the economy grew strongly and Brazil weathered the global financial crisis better than most nations.
He is loved within Brazil by the legions of poor, who consider the nation's first working-class president one of their own. His social programs and orthodox economic policies have helped lift 20 million people out of poverty and thrust another 29 million into the middle class.
Serra is a 68-year-old former governor of Sao Paulo state and one-time health minister who was badly beaten by Silva in the 2002 presidential election.
In the first round of the presidential election Oct. 3, Rousseff got 46.9 percent of the votes, falling just short of the majority needed to avoid a runoff. Serra finished second with 32.6 percent.
"I voted for Dilma because she is a fighter," said Estevam Sanches, a 43-year-old pizza parlor owner in Sao Paulo. "What we need is a fighter in the presidency to continue, as she says she will, with Lula's efforts to eradicate poverty and strengthen the economy."
Celia Montes, also voting in Sao Paulo, backed Serra because she said Silva's Workers Party has failed to make advancements in education, "and without a base of skilled labor we cannot build on the gains Brazil has made."
Rousseff was a key player in an armed militant group that resisted the 1964-1985 military dictatorship and was imprisoned and tortured for it. She is a cancer survivor and a former minister of energy and chief of staff to Silva.
Serra also battled the dictatorship, but through politics rather than armed resistance. He headed a national student group that opposed the regime and was forced into exile in Chile in 1965 before heading to the U.S., where he earned a doctorate in economics at Cornell.
Under President Fernando Henrique Cardoso, Silva's predecessor, Serra served as planning minister, then health minister, winning praise for defying the pharmaceutical lobby to market cheap generic drugs and free anti-AIDS medicine.
About 135 million voters were eligible to cast ballots Sunday.
Under Brazilian law, voting is mandatory for citizens between the ages of 18 and 70. Not voting could result in a small fine and make it impossible to obtain a passport or a government job, among other penalties.
