Mr Sanha has stood for president three times
Guinea-Bissau's former leader Malam Bacai Sanha has won a presidential run-off to decide who replaces assassinated ex-President Joao Bernardo Vieira.
Mr Sanha won 63% of the vote, defeating rival Kumba Yala, who has also served as president in the past.
Guinea-Bissau has a history of coups and its people have told correspondents they are tired of broken promises.
President Vieira was killed in March in apparent revenge for the death of the head of the army.
Mr Vieira led Guinea-Bissau for most of the period after independence from Portugal in 1974 - serving as president for a total of 23 years between 1980 and 2009.
Turnout among the country's 600,000 registered voters in last Sunday's run-off vote was estimated at about 60%.
The first round of polling on 28 June saw Mr Sanha win nearly 40% of ballots, 10% more than Mr Yala.
And election officials announced Mr Sanha had kept his lead in the second round of voting, clearly defeating Mr Yala.
When the two faced off in 2000, Mr Yala emerged as the winner.
In their final campaign rallies, both men repeated promises to bring peace and stability to the country.
Mr Sanha, who served as interim president from 1999-2000, was standing for the ruling PAIGC, the party of the 1970s struggle against Portuguese colonial rule.
This was the third time he had stood for president, having been defeated once by Mr Yala and in 2005 by Mr Vieira.
His motto is "Hora Tchica" - meaning "the time has come".
Mr Yala, who was overthrown in a 2003 coup, is the leader of the opposition PRS.
Analysts say many Bissau-Guineans hold him responsible for worsening the country's political and economic situation.
During his presidency the IMF and the World Bank suspended aid after accusations of mismanagement and a string of sackings in the government.
But he is believed to have wide support within the military.
Guinea-Bissau is cash-starved and heavily dependent on just one product - the cashew nut.
In recent years it has become a major transit point in drug smuggling between South America and Europe.