Dilma Rousseff has been re-elected president of Brazil, after securing more than 51% of votes in the closest election race in many years.
An official count showed her rival, centrist candidate Aecio Neves, taking just over 48% of the vote.
In her victory speech, Ms Rousseff said she wanted to be “a much better president than I have been until now”.
She faced protests last year against corruption, record spending on the football World Cup and poor services.
Ms Rousseff, who has been in power since 2010, is popular with poor Brazilians thanks to her government’s welfare programmes.
But the vote split Latin America’s biggest country almost evenly in two, along lines of social class and geography.
Ms Rousseff called on all Brazilians “to unite in favour of Brazil’s future” and said she would seek political reform.
“This president is open to dialogue. This is the top priority of my second mandate,” she told a cheering crowd in the capital, Brasilia.
She also thanked her supporters, especially her political mentor and predecessor Luiz Inacio Lula da Silva.
“I thank from the bottom of my heart our number one militant, President Lula.”
Her re-election for a second term extends the rule of her Workers Party (PT), which came to power in 2002 with President Lula.
Aecio Neves, of the Brazilian Social Democracy Party (PSDB), conceded victory in a speech to supporters in the southern city of Belo Horizonte.
He thanked the “more than 50 million Brazilians” who voted for him and said he had telephoned the re-elected president.
“I… wished her success in the administration of her next government, and I reaffirmed what I feel should be our greatest priority, to unite Brazil on the basis of an honourable project which dignifies all Brazilians,” he said at the rally.
Mr Neves was the governor of the southern swing-state of Minas Gerais for eight years.
Both he and Ms Rousseff had made economic growth and lifting Brazilians out of poverty central to their election campaigns.
The election came after weeks of intensive campaigning by the two candidates and a presidential race that took a tragic turn after Eduardo Campos, a main opposition candidate, was killed in a plane crash in August.
His running mate, a renowned environmentalist, Marina Silva, was thrust into his place, vowing to become the South American country’s first “poor, black” president.
But she came third in the first round after Ms Rousseff and Mr Neves secured 41.5% and 33.5% of the vote respectively.
As neither candidate got an absolute majority, the election went into a second round.