The inauguration took place in Samuel Kanyon Doe stadium near the capital, Monrovia, in the presence of several African heads of state and friends and former colleagues from his football years.
He was sworn in by the chief justice of the Supreme Court, Francis Korkpor, to the cheers of the crowd that filled up the 35,000 capacity stadium.
With his inauguration, Weah becomes the 25th president of the West African nation, taking power from President Ellen Johnson Sirleaf after 12 years.
Electoral victory
Weah beat Sirleaf's Vice President Joseph Boakai in December 2017's run-off election, gaining 61.5% of the ballot against 38.5% for his rival and winning in 14 of Liberia's 15 counties.