We reached agreement with Fulham for the signing of the Belgium international on Wednesday.
Mousa has won many admirers with his performances for the Cottagers – the latest a man-of-the-match display against Manchester United at Old Trafford on Saturday.
Now he’s looking forward to a new chapter in an already-impressive career.
“I'm happy to join Spurs, it's a fantastic club,” said Mousa, a Dutch title-winner with AZ Alkmaar in 2009.
“You can see over the last few years that Spurs have played well, everybody knows it's a good team and a good club and that's why I wanted to come here.
“The club has plans to do lots of good things and that's why I want to be a part of it.”
Mousa is looking forward to linking up with Belgian international team-mate Jan Vertonghen – and the pair go back a long way.
“I know Jan from when I was 10 years old, we played together then,” he added. “I know him well, he's a great guy and he's said a lot of good things about this club.
“He says there are friendly people here and for me, that's very important, to feel great somewhere. I'm sure I will here.”
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