At the end of 2014 he signed his first professional contract with French club Rennes. He made his Ligue 1 debut at just the age of 17 and he scored his first goal against Girondins. His progress attracted the attention of Borussia Dortmund and he signed for the Bundesliga club in the summer of 2016. Dembélé adapted quickly to German football, scoring 12 goals and providing 20 assists in his first season.

He signed a five year deal with FC Barcelona in the summer of 2017. He made his Barça debut on 9 September in the league against Espanyol and celebrated by providing an assist. He scored his first goal as a blaugrana against Chelsea in the Champions League of that season. 

In the 2021/22 season, Dembélé stood out as leader in assists in La Liga. After gaining the confidence of coach Xavi Hernández, the Frenchman had an excellent campaign, forming a great partnership with Aubameyang. The winger provided 13 assists and in the summer of 2022 with his contract at an end, Dembélé extended his stay with the blaugranes until June 2024. 

After representing France at various youth levels, he is a current France international and formed part of the 2018 World Cup winning squad in Russia alongside his blaugrana team mate Samuel Umtiti.