With most ballots from Tuesday's run-off vote counted, Mr Weah is well ahead of opponent Joseph Boakai.
He will succeed Ellen Johnson Sirleaf, Africa's first elected female president, in Liberia's first democratic handover in decades.
Mrs Sirleaf defeated Mr Weah in the presidential election run-off in 2005, after the end of a brutal civil war.
As news of Mr Weah's victory emerged on Thursday, his supporters began celebrating in the capital Monrovia.
