Sounders FC owner and general manager Adrian Hanauer issued a club statement to confirm the completion of the deal.
"We are extremely proud of what DeAndre has accomplished in his young professional career. His success is a reflection of his individual ability as well as soccer development in Washington State and the continued commitment to progress the sport in this country.
"DeAndre is and always will be a special member of the Sounders FC family, and we are excited to have him in Seattle for the remainder of the season."
Yedlin, who flew over to London last week to have a look around the training complex, also confirmed the move to Tottenham and that he was remaining at Seattle Sounders for the remainder of the MLS season.
"I first want to thank everyone involved in my development. From my family to youth coaches to the Sounders, I am lucky to have such a strong support system.
"I'm excited to have the opportunity to play with Spurs in the English Premier League, and I look forward to helping the Sounders win a championship this season.
"It’s a great team with a new coach and a style that suits the way I play. That’s a big reason I made the decision.
"The facilities are the best in Europe, if not the world. It’s a great team. I’m very excited.
"I’ve talked to Jürgen Klinsmann a lot about this move and he supports it, which was one of the big reasons behind the decision."
Yedlin has signed a 4-year contract and joins prior to the 2015/16 season after finished the MLS season in a deal worth a reported £2.4 million (€2.99m - $4m) by American media.
He has been dismissed in some circles as a marketing gimmick and that his talents aren't good enough. These people clearly haven't seen him lay and are simply making an opinion because he plays in the MLS. If you look at his stats he has only been booked twice in 14 MLS games (1,229 minutes) suggesting he keeps his head and doesn't make rash challenges.
480 successful passes from 586 attempts for an 81.9% success rate for a full-back who crosses the ball. Of those 390 were forward passes, 15 of those were 'key' passes and he has created 15 chances.
In 14 games he has had 4 shots and not scored. He has won and lost 30 tackles and beats his man 52.94% of the time. He wins 60% of his aerial duels.
He has made 35 interceptions, 6 blocks and 47 clearances and made 1 defensive error.
In the World Cup he made 3 appearances having only made his international debut in January, from those 3 games he created 3 chances. However he only played 18 minutes verses Portugal, 6 minutes against World Cup winners Germany (right midfield) and 88 minutes including extra-time against Belgium. So he played 112 minutes or 1 full game and 22 minutes from which he created those 3 chances.
His pass accuracy at the World Cup was 76%, his average pass length 17m and he won 67% of all his duels with no defensive errors.
Like any player the are aspects of his game to work on but he has pace, he can cross a ball, he loves to get forward, all the things a modern full-back needs. Their secondary skill it would seem is defending and he'll have to learn as he steps up in grade but at only 21 has time to do so.
He will of course be valuable for expanding the Tottenham name but that only makes a major difference if the player in question is playing a significant part at the club. He is an American star, one of their young hopes so for him to be of maximum commercial value to us he needs to be playing in the Premier League and making a contribution to the matches that matter. That won't happen overnight but he has been signed as a footballer, to dismiss him as simply anything else is probably an opinion formed, as I say, through a lack of understanding.