The South Korea international has scored 47 goals in 140 appearances for Spurs since joining from Bayer Leverkusen in 2015.
The 26-year-old forward’s new contract ends in the summer of 2023.
Son becomes the latest high-profile name to commit his future to Spurs, with Harry Kane and Mauricio Pochettino also signing new long-term deals in recent months.
Tottenham have also confirmed Son will miss part of the season to represent South Korea at the Asian Games.
The tournament begins on August 14, just four days after the 2018/19 Premier League campaign kicks off.
The Asian Games is not an official FIFA tournament and clubs are not required to give permission for players to join up with their national sides.
However, winning a gold medal would boost Son’s hopes of avoiding or reducing his military service, which is compulsory for young men in South Korea.
Speaking on Sky Sports News, former Tottenham midfielder Ryan Mason said: “I think it’s massive for Tottenham. In recent years they haven’t hesitated to sign up players that warrant new contracts to long-term deals.
“He’s scored lots of goals, he’s assisted a lot and his overall performances have been outstanding.
“He is key to the way Tottenham play and the way they go about things so I’m very happy to see that.”
Mason believes Liverpool have done the best business in the transfer market so far, paying £67m to make Alisson the world’s most expensive goalkeeper, and he is hoping Spurs bring in some high-profile players as well.
“I would like to see Tottenham get one or two players,” he added. “There’s lots of talk about certain individuals. Jack Grealish and Wilfried Zaha are the type of players I would love to see at Tottenham.
“I feel like they fit the philosophy and the way the gaffer and the club like to do things. They’re young and they know the Premier League as well.”