"Timothy's a young talent who is (a) full international player. He has a long career ahead of him but he has those natural attributes in terms of his pace and technique," Celtic manager Brendan Rodgers said in a statement. "He's hungry too."
While he will spend the second half of the 2018-19 season away from the Parc des Princes, PSG announced Weah signed a one-year extension as a precursor to the loan move, keeping him in Paris until 2021.
Weah, 18, progressed through PSG's youth ranks but has struggled to crack the club's star-studded first team this season. Though he impressed in the side's preseason matches, he hasn't made a Ligue 1 appearance since the second match of the campaign against Guingamp.
Though his time with his parent club has been sparse, the touted youngster earned his first of eight international caps in March in a 1-0 win over Paraguay. He won his first start for the USMNT in May, scoring the final goal in a 3-0 friendly win over Bolivia.
Weah is the son of legendary retired striker George Weah, who made history in 1995 when he became the only African player to ever win the Ballon d'Or. The 52-year-old now serves as President of Liberia.