A title-winner during his time at Ajax and Atletico, where he also reached the Champions League Final in 2014, Toby has signed a contract with the club until 2020.
He arrives at White Hart Lane following an impressive season in the Premier League on loan at Southampton.
“I’m very proud to become a Spurs player,” said Toby, now capped 47 times by Belgium. “I’m very happy to be here and I hope to have a wonderful time with this team.
“From the beginning I knew a lot about it (the club) from Jan Vertonghen, Mousa Dembele and Nacer Chadli.
“It’s a big club and it’s always been a dream to play at a club like Spurs. Now that dream is coming true so I’m very happy, very proud and I will give my best.”
Toby has a head start at his new club with those familiar faces of Jan, Mousa and Nacer plus Christian Eriksen, who he played with alongside Jan at Ajax.
“I know the players from the national team and I played with Jan at Ajax, we had a central defensive partnership,” he said.
“It’s nice when you join another club that you know a couple of players. I hope to get to know them a little better now.”
He also knows plenty about the current squad having played twice against us last season as he racked up 28 appearances for the Saints – we won 1-0 at the Lane in October before a 2-2 draw at St Mary’s in April.
“There is a lot of quality in the team and good, young players the club also wants to develop,” he added. “Those two games were very tough for us, Spurs had a very good team.
“I’m really looking forward to helping the team reach the goals we will set.”
Follow @SpursOfficial on Twitter to find out how you could win Toby’s signed Spurs shirt later today (Wednesday, July 8).