Weah was born and raised in the Clara Town district of Monrovia.
After playing in the Liberian domestic league at the beginning of his successful career and winning several national honours (including the Liberian Premier League and the Liberian Cup), Weah's abilities were discovered by the Cameroon national team coach, Claude Le Roy, who relayed the news to Arsène Wenger. Weah moved to Europe in 1988, for just £12,000 from Cameroonian club Tonnerre Yaoundé, when he was signed by Wenger – the manager of Monaco at the time – who flew to Africa himself prior to the signing, and whom Weah credits as an important influence on his career.
During his time with Monaco, Weah won the African Footballer of the Year for the first time in 1989; this was his first major award and he took it back home for the entire country to celebrate.
Weah subsequently played for Paris Saint-Germain (1992–95), with whom he won the Coupe de France in 1993 and 1995, the French league in 1994, and the Coupe de la Ligue in 1995 during a highly prolific and successful period; he also became the top scorer of the 1994–95 UEFA Champions League, with seven goals, after reaching the semi-finals with the club.
In 1994, he won the African Footballer of the Year Award for the second time in his career.
Weah won the African Player of the Year Award for the third time in his career, and was named to the Onze de Onze by the French football magazine Onze Mondial.
Weah joined A.C. Milan in 1995, with whom he immediately won the Italian league in 1996 under Fabio Capello, playing alongside Roberto Baggio and Dejan Savićević in Milan's attack, as well as Marco Simone, on occasion, and finishing the season as Milan's top goalscorer; he won the Serie A title once again in 1999.
Due to his performances with both Paris Saint-Germain and Milan, in 1995 Weah won the Ballon d'Or.
Weah was banned from six European matches for breaking the nose of the Portuguese defender Jorge Costa on 20 November 1996 in the players' tunnel after Milan's draw at Porto in the Champions League.
Weah signed for Premier League club Chelsea on loan from Milan on 11 January 2000, in a deal which would keep him with the West London club until the end of the 1999–2000 English season. Although past his prime, Weah's time in England was deemed a success, especially at Chelsea where he instantly endeared himself to their fans by scoring the winner against rivals Tottenham Hotspur on his debut, and scored further league goals against Wimbledon and Liverpool. He also scored twice in Chelsea's victorious 1999–2000 FA Cup netting crucial goals against Leicester City and Gillingham. This led to him starting in the final, which Chelsea won 1–0.
Chelsea manager Gianluca Vialli did not make Weah's move permanent, and, on 1 August 2000, he officially left Milan, and signed for newly promoted English Premier League side Manchester City on a free transfer on a two-year contract worth £30,000 a week, declining the offer of a £1 million pay-off from Milan owner Silvio Berlusconi.
Following his time in England, Weah returned to France and had a spell at Marseille, where he remained until May 2001.
He later played with Al-Jazira in the UAE Pro-League, where he remained until his retirement as a player in 2003, at age 37.
Following the end of the Second Liberian Civil War, Weah announced his intention to run for President of Liberia in the 2005 elections, forming the Congress for Democratic Change to back his candidacy. Weah obtained a plurality of votes in the first round of voting on 11 October, garnering 28.3% of the vote. This qualified him to compete in a run-off election against Sirleaf, the second placed candidate.
Weah lost the run-off to Sirleaf on 8 November, garnering only 40.6% to 59.4% for Sirleaf. Weah alleged that the election had been rigged through voter intimidation and ballot tampering, and many of his supporters protested the results in the streets of Monrovia. However, after assurances that the vote was fair, several prominent African leaders called on Weah's supporters to accept the result with grace and dignity, and Sirleaf became President. The African Union had characterized the elections as "peaceful, transparent, and fair".
Weah also remained active in Liberian politics, returning from the United States in 2009 after getting a degree in business administration at DeVry University in Miami to successfully campaign for the Congress for Democratic Change candidate in the Montserrado County senatorial by-election.
In 2014, he ran for election to the Senate as a Congress for Democratic Change candidate in Montserrado County. He was overwhelmingly elected to the Liberian Senate on 20 December 2014. Weah defeated Robert Sirleaf, the son of President Sirleaf, becoming the first Liberian international athlete elected to represent a county in the Legislature. He won a landslide victory, receiving 99,226 votes, which represented 78.0% of the total votes from the 141 polling centers.
Weah announced his intention to run for President of Liberia in the 2017 elections, standing for the Coalition for Democratic Change. Weah won the first round of the 2017 election with 38.4% of the vote.
After winning the first round of the 2017 election, Weah and Joseph Boakai of the Unity Party went into the second round of the election. In the second round, Weah was elected President of Liberia, winning a run-off against Vice President Joseph Boakai with more than 60% of the vote.
Weah was sworn in as president on 22 January 2018, making him the 4th youngest serving president in Africa, marking Liberia's first democratic transition in 74 years.
On 29 January 2018, in his first annual message to the national legislature, he reduced his salary and other benefits by 25% with immediate effect. "With the assessment that I gave you earlier of the poor condition of our economy, I believe that it is appropriate that we should all make sacrifices in the interest of our country. According to Article 60 of the Constitution, the salaries of the President and the Vice President are established by the Legislature, and cannot be increased or reduced during the period for which they are elected. However, in view of the very rapidly deteriorating situation of the economy, I am informing you today, with immediate effect, that I will reduce my salary and benefits by 25% and give the proceeds back to the Consolidated Fund for allocation and appropriation as they see fit."
On 21 February 2018, Weah made his first official visit outside Africa, to France, meeting French President Emmanuel Macron. The meeting focused on improving the relationship between France and Liberia and also sought French help for a sports development project in Africa.The meeting was also attended by Didier Drogba, Kylian Mbappé and FIFA president Gianni Infantino.
Weah returned to the national team for a specially arranged friendly against Nigeria on 11 September 2018, his final international appearance, playing at the age of 51 while in office as the country's president. His number 14 shirt, worn by Weah at his playing peak, was retired after the friendly, with Weah receiving a standing ovation when he was substituted.