Dembele, who won the Dutch league with Alkmaar in 2009, also played for Fulham before a seven-year spell with Spurs, featuring in 249 matches in all competitions and scoring 10 goals for the London club. He joined Guangzhou City in 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 Instagram.
Dembele made his Belgium debut in 2006 and played 82 games for his country, featuring at two World Cups and Euro 2016. The high point of his international career was winning in the 2018 World Cup third-place playoff game against England.
He retired from international football in March 2019.
"Congratulations on an incredible career, Mousa. Enjoy your retirement," Tottenham said on Twitter.