The National Elections Commission said that with more than 90 per cent of votes counted, Ms Johnson-Sirleaf had 59.1 per cent of the ballot. Her rival, the millionaire football star George Weah, had 40.9 per cent from Tuesday's election in the west African state.
"I think the trend is now irreversible," said 67-year-old Ms Johnson-Sirleaf, known in Liberia as the Iron Lady. "Just my own performance ... is going to raise the participation of women not just in Liberia but also in Africa."
The presidential run-off was given a generally clean bill of health by international observers who monitored the ballot in Africa's oldest independent republic, founded by freed American slaves in 1847. The US State Department spokesman Adam Ereli said: "On the whole it was an orderly and efficient process."
The capital, Monrovia, was calm yesterday, but UN peacekeepers had used batons on Wednesday night to break up a crowd of angry Weah supporters complaining of fraud.
The count is expected to be completed within the next few days.
Ms Johnson-Sirleaf, a Harvard-educated banker and economist, polled just 19.8 per cent in the first-round election on 11 October and trailed Mr Weah by 10 points going into the second-round vote. But after a lavishly funded and aggressive burst of late campaigning, she looked yesterday to have prevailed in her quest for the office that eluded her in 1997, when the warlord Charles Taylor romped to victory after a seven-year rebellion. Much of her late surge may have been due to a media blitz that hammered away at Mr Weah's lack of formal education and his political inexperience, amid a whispering campaign which exploited the ethnic tensions that simmer below the fragile peace after two civil wars. Ms Johnson-Sirleaf has compiled a resumé of domestic and international experience that would be some comfort to Liberia's development partners eager to help it reassume its position among Africa's most prosperous nations. She served in, and then opposed, the successive administrations of presidents William Tolbert and William Tubman before turning down a senate seat in the 1985 government of Samuel Doe, a move that saw her jailed for the first time on charges of treason. She was jailed again for her alleged involvement in a failed coup later that year by Thomas Quiwonkpa, prompting her to leave the country before returning to stand against Taylor in 1997.
Stints at Citibank, the World Bank and within the United Nations system have also given the widowed grandmother insight into how to unite and rebuild a country without running water or electricity, a good road network or enough jobs or seats in classrooms for its 3 million people.
"When I look back on my life story, I see a life filled with activism, and if I have courted controversy, it is only because I have tried to be consistent in my political beliefs," she said in a pre-election interview. "I think I have consistently taken the position that best serves the national interest, so for me it was not about switching sides but staying true to what I thought was best for the Liberian people."
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