The 21 year-old centre back who already has an international cap to his name has made the risky move to Cardiff in order to increase his chances of a spot on the England squad for the World Cup next year.
In order to be looked to get a place in the England side, he will need regular football and will do so this season so long as there is no injuries.
He joins the Welsh club for a club record £8million after making 28 appearances for the Spurs last season including 18 Premier League appearances.
Cardiff have also signed Danish striker Andreas Cornelius, full-back John Brayford and also keeper Simon Moore during the summer window.