The American international - who made 224 appearances for Fulham, scoring 60 goals.- had been heavily linked with a move to Liverpool, while it is reported that Aston Villa also enquired about the availability of the 29-year-old.
A statement on the Fulham website read: "Fulham Football Club can confirm that, on Friday evening, Clint Dempsey joined Tottenham Hotspur. Clint was a very influential player for Fulham over a number of seasons and the Club thanks him for his contribution and wishes him well for the future."
Dempsey had been hankering after a move to Liverpool all summer, but he is now more than happy to have signed for Tottenham.
"To play under this head coach and play for this club is a dream come true. I want to make the most of it," Dempsey said on Tottenham's Twitter feed.
"There are a lot of great players here, I'm looking forward to training and playing with them."
Watch: Spurs strengthen on deadline day... More Videos
Dempsey had not played for Fulham this season after it became clear he wanted a move, but he added on Tottenham's website: "A lot was said and written ahead of me leaving Fulham. It wasn't how it was portrayed, but that's in the past now and we move on.
"I want to thank the fans for everything, some of the best memories I've had in football, and thank the chairman for giving me the opportunity to come from the MLS and compete over here.
"All I can say is thank you and now I'm looking forward to the next challenge."