Son joined Tottenham from Bayer Leverkusen in 2015 and has made 454 appearances for the club, scoring 173 goals.
At the age of 33, Son is set to join Los Angeles FC in the MLS, with negotiations at an advanced stage.
He made the announcement at a media conference in Seoul, where Tottenham will play a preseason friendly against Newcastle on Sunday.
Son expressed his gratitude to the fans, saying, "I want to say thank you to all the Spurs fans for giving me so much love. I hope the goodbye is also good timing and this is the right time to make that decision."
Spurs manager Thomas Frank praised Son, stating, "He is a true Spurs legend in every aspect, one of the greatest players to play in the Premier League."
