The 22-year-old initially agreed to move to White Hart Lane in the summer when his contract was set to expire, but Spurs pushed through a 1.75 million euro deal for the midfielder with Sandro facing a lengthy spell on the sidelines.
"As soon as I saw the facilities, the crowd and spoke to Andre I just knew I wanted to be here,” he told the club's official website. "The facilities are the best I've seen. I'm proud to be here, a huge club that is only getting bigger and bigger."
The Germany international is looking forward to the new challenge of settling in to the club midway through the season.
"It's fantastic to be here. I can't wait to settle and to play for the club and I'm looking forward to the season," Holtby said. "I played Champions League with Schalke but I wanted to be here now. I've been checking the club and Premier League on Twitter and YouTube, I've got the app! As footballers say, I'm over the moon to be here!"