The 26-year-old signed a five-year deal with the north London club and is Spurs' third signing of the summer transfer window following the permanent arrivals of Dejan Kulusevski and Guglielmo Vicario.
Spurs have been tracking Maddison for several seasons and ESPN reported earlier this month that the club entered into advanced talks with Leicester for the midfielder after new head coach Ange Postecoglou indicated his approval for the move.
Maddison joined Leicester from Norwich City in 2018 and made 203 appearances for the club in all competitions, scoring 55 goals and making 41 assists.
The midfielder was included in England's squad for last year's World Cup in Qatar but a knee injury meant he did not feature in the tournament as Gareth Southgate's team were knocked out in the quarterfinals by France.
Meanwhile, Spurs' all-time record goal scorer, Harry Kane, has been told by the club that he is not available for transfer this summer, sources have told ESPN, despite Bayern Munich stepping up their interest in the England captain.