Dembele, who also had spells at Dutch club AZ Alkmaar and English side Fulham, enjoyed his most successful years at Spurs, playing 181 matches between 2012 and 2019 and scoring seven goals for the London club. He joined Guangzhou City in 2019.
He made his Belgium debut in 2006 and played 82 games for his country, featuring at two World Cups and Euro 2016 before retiring from international football in March 2019.
"I still have a year on my contract left. But I can already share I will stop my career after this year is finished," Dembele wrote on his Instagram account.
"Congratulations on an incredible career, Mousa. Enjoy your retirement," Tottenham said on Twitter.
