Weah took his oath of office at exactly noon inside the 35,000 capacity Samuel Kanyon Doe Sports Complex in Monrovia.
He will succeed Ellen Johnson Sirleaf, Africa's first elected female president.
Weah won presidential elections a year ago to emerge the successor to Sirleaf beating then vice president Joseph Boakai twice in a space of three months.
According to Liberia's National Election Commission, Weah got 61.5 percent of the votes in the run-off held in December.
George Weah, the former World Footballer of the Year and president-elect, had already alighted in his bright red football kit.
"I fully believe that the overwhelming mandate that I received from the Liberian people is a mandate to end corruption in public service; I promise to deliver on this mandate", he said.
The new President extended hands of fellowship to all his country men and women, noting that they all have to work together to give the country a new position of prestige in the community of nations. It is the first democratic transfer of power in the West African state in more than 70 years.More news: Federal Bureau of Investigation did not save officials' texts during Trump probe
The 51-year-old is regarded as one of the greatest African players of all time and of course is still making time for football.
Arsenal boss Arsene Wenger has likened Weah's life to a film script, while the former striker has described Wenger as a "father figure" who stood by him as he faced racist attacks in Europe.
He signed for Milan in 1995 where he spent four successful seasons, winning Serie A twice.
"The Prime Minister of Senegal will represent his country". Weah was subsequently elected to the Liberian Senate for Montserrado County in the 2014 elections.
He became involved in politics in Liberia following his retirement from football.
"This means tangible change in terms of visible civil infrastructure, and it means more jobs and opportunity", she said.