Malam Bacai Sanha has won Guinea-Bissau's presidential election, four months after the country's leader was assassinated.

Sanha, a former head of state, won 63 per cent of the vote, beating Kumba Yala, his opponent, who took 36 per cent.

The new leader represents the African Party for the Independence of Guinea and Cape Verde (PAIGC), Guinea-Bissau's biggest political party.

It is hoped his election will bring stability to the coup-prone West African nation, Desejado Lima da Costa, the country's electoral chief said.

"These elections are very important for Guinea-Bissau because they will enable the consolidation of democracy and credibility ... and enable stability and development," da Costa said.

Revenge attack

Sanha, 62, was interim president for a year following a 1998-1999 civil war, while Yala was elected president in 2000, but overthrown in a bloodless coup three years later.

The vote was triggered by the killing of Joao Bernardo Vieira, Guinea-Bissau's long-time president, by soldiers on March 2, in an apparent revenge attack following the assassination of army chief General Batista Tagme Na Waie in a bomb attack.

In June, the army killed two senior political figures in what they claimed was an operation to foil a coup plot.

The murder of Vieira, who ruled Guinea-Bissau for much of the past 25 years, came about a decade after the military ousted him during a previous term as president.

The run-off round was originally to have been held on August 2 but was brought forward to encourage a higher turnout as the later date could have interfered with harvest work in the predominantly rural country.

Since gaining independence from Portugal 35 years ago, Guinea-Bissau has experienced numerous coups, countercoups and a civil war.