The electoral board confirmed Weah's run-off victory on Friday evening.
- He will replace Ellen Johnson Sirleaf, who in 2006 took the helm of the West African country first founded for freed US slaves.
- Weah's former club Paris Saint-Germain tweeted its congratulations to the "world football legend".
Liberians and international football stars have joined together in celebrating George Weah's presidential victory in the country's first democratic transfer of power in decades, as the former striker vowed to usher in a period of change.
Idolised in Liberia as "Mister George", Weah is to be sworn in on January 22, replacing Ellen Johnson Sirleaf, who in 2006 took the helm of the West African country first founded for freed US slaves.
The electoral board confirmed Weah's run-off victory on Friday evening, as his rival, Vice President Joseph Boakai, conceded defeat.
Weah, 51, who starred in top-flight football at Paris Saint-Germain and AC Milan in the 1990s and briefly at Chelsea and Manchester City before entering politics in 2002, won 61.5 percent of the ballot, taking 14 of Liberia's 15 counties.
"My fellow Liberians, I deeply feel the emotion of all the nation. I measure the importance and the responsibility of the immense task which I embrace today. Change is on," Weah said on Twitter.
However, a victory speech was postponed after crowds of energetic supporters gathered around a podium for Weah's address grew too boisterous, an AFP correspondent said.
Boakai said he had called Weah to congratulate him and appealed for unity, saying: "My love for the country is far (more) profound than my desire for the presidency."
The White House called the vote "a major milestone for Liberia's democracy" while UN Secretary-General Antonio Guterres applauded "all Liberians for the successful completion of the elections process, which was conducted in a peaceful environment".
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The tumultuous events of the past 70 years in Liberia, where an estimated 250,000 people died during back-to-back civil wars between 1989 and 2003, have prevented a democratic handover from taking place since 1944.
Sirleaf's predecessor Charles Taylor fled the country in 2003, hoping to avoid prosecution for funding rebel groups in neighbouring Sierra Leone.