Dembele joined the Scotish giants at the age of 10 and made global headlines when he made his U20 debut with the development side in 2016 amongst players seven years his senior.
His rise to prominence has seen an international tug-of-war ensue between England, Scotland and Ivory Coast and the winger has since represented the European nations at U15 and U16 level respectively.
"I'd like to say thank you to everyone, and I'd like to thank everyone for everything they've done for me," he told the club's website after signing a deal that will run until the end of the 2020/21 season.
— Celtic Football Club (@CelticFC) December 24, 2018
"Getting attention at a young age has been hard, but I've obviously had my family to help me through that. You need to be strong mentally, you need to stay grounded, and you just need to get on with everything that you do on a daily basis.
"My goal is to play for the first team," the 15-year-old added. "As soon as I can, I’m going to try to get into the first team, 100 per cent.
"In the Reserves, every training session, every game – it's all to prove myself to the manager that I can play in the first team."