Brazilian President Luiz Inacio Lula da Silva has been re-elected in a clear victory, polling more than 60% of the vote against rival Geraldo Alckmin.
President Lula was cheered by supporters after voting in Sao Paulo
In a victory speech, Lula said he would govern for all Brazilians and intensify efforts to alleviate poverty during his second four-year term.
"We will give attention to the most needy. The poor will have preference in our government," he said.
Lula narrowly failed to win in the first round, forcing Sunday's run-off.
In a speech in Sao Paulo, Lula promised to boost growth and reduce inequality to put Brazil on track to reach the ranks of developed nations.
"The foundation is in place, and now we have to get to work," he told crowds of supporters who had taken to the streets in celebration, waving Workers' Party flags.
Supporter Danusia Alves said: "For me it is a great happiness because we have a wonderful government. The people who were never taken care of now are being taken care of."
Votes in Sunday's run-off were cast using electronic ballot boxes, allowing officials to deliver a swift result.
A partial count showed the incumbent president had 60% of the vote - an insurmountable lead. Shortly after, the head of Brazil's electoral court declared Lula re-elected.
Corruption scandals hampered President Lula's campaign
The BBC's Steve Kingstone in Sao Paulo says it is a resounding victory for a man who was written off by many just over a year ago, when his Workers' Party was at the centre of a cash-for-votes scandal.
But Lula weathered that storm and another during the first phase of this campaign when party colleagues were again accused of corruption, our correspondent says.
Lula narrowly failed to win outright in the first round of voting on 1 October.
During the ensuing campaign the president suggested to voters that Mr Alckmin might scrap welfare benefits for the poor and privatise Brazil's remaining state companies.
Privatisation is generally viewed with suspicion in Brazil. Despite repeated denials by Mr Alckmin, the accusation undoubtedly cost him votes, our correspondent adds.