Former football star George Weah has defeated Vice President Joseph Boakai to win Liberia's presidential run-off election with 61.5 per cent of the vote based on 98.1 per cent of ballots cast.

Weah will succeed incumbent President Ellen Johnson Sirleaf next month in what will be Liberia's first democratic transition since 1944.

Supporters of the 51-year-old paraded through the streets of the capital Monrovia and honked car horns to celebrate the news.

Weah grew up in Clara Town slum in Monrovia and went on to star for AC Milan, Paris Saint-Germain and Chelsea and become the only African to win FIFA World Player of the Year.

His rags to riches story helped him tap into dissatisfaction with Johnson Sirleaf's 12-year tenure, which drew a line under years of civil war but was criticised for failing to root out elite corruption or persistent poverty.

Turnout for the second round stood at 56 per cent, National Election Commission (NEC) Chairman Jerome Korkoyah told reporters in Monrovia.

Liberia is Africa's oldest modern republic and was founded by freed US slaves in 1847. Its last democratic transfer of power occurred in 1944 and was followed by a military coup in 1980 and a 14-year civil war that ended only in 2003.

The US-based Carter Centre said there were "notable improvements" in the handling of Tuesday's vote from the first round in October, echoing positive assessments from other international observers.