A year later, he transferred to Barcelona for an initial fee of €105 million, becoming at the time the joint-second most expensive footballer ever, alongside compatriot Paul Pogba.

[7][8] Dembélé made his senior debut for Rennes' reserve side in the Championnat de France Amateur, on 6 September 2014, coming on as a 78th-minute substitute for Zana Allée.

[9] On 9 November, he scored his first career goal, again coming off the bench in a game at the Stade de la Piverdière, this time against the reserves of Laval.

[11] On 6 November 2015, Dembélé made his professional debut for Rennes' first team in Ligue 1 against Angers, replacing Kamil Grosicki for the last five minutes of the game.

[15] Rennes' sporting director Mikaël Silvestre compared Dembélé to Cristiano Ronaldo, who he had seen arrive at Manchester United around the same age.

[18] On 22 November, he scored the first Champions League goal of his career as the German club defeated Legia Warsaw 8–4 in a group stage meeting.

[19] On 26 April 2017, Dembélé assisted Aubameyang's goal and scored the 74th-minute winner against Bayern Munich in the DFB-Pokal's semi-final, helping Dortmund reach the cup final.

[20] In the decisive game on 27 May, he scored the first goal of a 2–1 victory as Dortmund clinched their first major title in five years by winning the 2017 DFB-Pokal Final against Eintracht Frankfurt.

[26] Barcelona had just sold Neymar to Paris Saint-Germain (PSG) for €222 million, so the deal meant that Dembélé became the joint-second most expensive player (in euros), along with Paul Pogba.

[28][29] Dembélé made his debut on 9 September as a 68th-minute substitute for Gerard Deulofeu in a 5–0 Derbi barceloní win over Espanyol at the Camp Nou, assisting the final goal by Luis Suárez.

[36] Dembélé won both the Copa del Rey and La Liga winners' medals in his first season in Spain, with the 20-year-old scoring four goals in 24 appearances across all competitions.

[41] On 11 December, he scored a remarkable solo goal against Tottenham Hotspur outpacing many defenders, finishing with a cool left footed shot past Hugo Lloris.

[42] After the match, Barcelona manager Ernesto Valverde praised the youngster, saying "He has made a great goal, within reach of players with his talent.

[44] Dembélé injured his left hamstring in the opening match of the 2019–20 La Liga season, a 0–1 defeat against Athletic Bilbao, and was expected to miss five weeks.

[65] In the second leg six days later, he scored PSG's first goal in a 4–1 away victory, helping secure his club's qualification to the semi-finals and taking home the player of the match award.

[72][73] Dembélé was called up to the senior France squad for the first time in August 2016 to face Italy and Belarus in friendlies after Alexandre Lacazette and Nabil Fekir withdrew through injury.

[78] Dembélé was called up to the French squad for the 2022 FIFA World Cup in Qatar, where he played all games as France finished the tournament as runner-ups.

[89] In July 2021, video footage of Dembélé along with teammate Antoine Griezmann circulated online, in which he was seen making racial comments against the Japanese technicians in their hotel room.

[90] As the technicians appeared to be troubleshooting the room's television, Dembélé made comments towards Griezmann in French, stating "All these ugly faces, just so you can play PES, aren't you ashamed?