Liberia's president-elect has pledged to make women across the world "proud", after becoming Africa's first elected female head of state.
The president-elect pledged to fight corruption and create jobs
Ellen Johnson-Sirleaf said her election victory had "shattered the glass ceiling theory".
Addressing the nation after her win was confirmed, she promised to usher in a new era after 14 years of war.
The Harvard-educated economist beat former football star George Weah in an election run-off.
Mr Weah alleged the run-off vote was rigged but international observers say the poll was largely free and fair.
South Africa's President Thabo Mbeki said Mrs Johnson-Sirleaf's election was "a beacon of hope for women in Africa and the world in general."
Liberia's president-elect herself said: "I have the obligation to bring pride to the women of Liberia, Africa and the entire world."
"Today marks the beginning of a new era, the dawn of a new day for our nation after so many years of turmoil and instability."
She also pledged to fight corruption, create jobs and restore electricity and water supplies.
The polls were the first for eight years, and the first since Liberia emerged from 15 years of civil war.
The announcement of Mrs Johnson-Sirleaf's win is a symbolically crucial day for Liberia, says the BBC's world affairs correspondent Mark Doyle.
She is nicknamed The Iron Lady, but has promised to show a new, softer side as president.
The official results came some two weeks after the polls took place partly because of the logistical difficulties of collecting and checking results from remote jungle locations.
Mr Weah's supporters, who include many fighters demobilised after the civil war, have taken to the streets several times this month to protest over alleged voting fraud. Street protests have now been banned.
Top officials from Mr Weah's party have said they will take their case to the Supreme Court if an electoral commission, which is still investigating, finds no evidence of fraud.
The election was organized and its security guaranteed by a 15,000-strong UN peacekeeping force.
Our correspondent says most Liberians believe a free poll in their war-ravaged country would have been impossible without the UN presence.
The head of the UN mission says the task at hand now is reconciliation and reconstruction.
After a quarter of a century of war and misrule, Liberia's road network is in ruins, there is no national telephone network and no national electricity grid.