Spurs are reported to have paid a fee of 60m Euros with manager Thomas Frank hoping the 22-year-old's creativity will help "unlocking defences" of opponents.
Simons, who will wear the number 7 shirt at Tottenham, scored 22 goals and assisted 24 others in 78 appearances for German side Leipzig, who he joined on loan from Paris St-Germain in 2023 before signing permanently in January of this year.
He has also scored five goals in 28 appearances for the Netherlands, having made his debut at the World Cup in Qatar in 2022.
Simons said: "I'm really happy and can't wait to get going. I've been dreaming of this for a long time. It's a great Club and when I met the Head Coach I knew straight away that this was the right place for me.
"I will bring flair to the team but also hard work and discipline. I want to do everything I can to win, for the team and also for the fans."
Frank added: "I'm really pleased we have brought Xavi in - he is a great addition to the squad. He is still young, however he already has good experience and, over the past few years, has played a lot of games at the top level.
"Xavi has proven his ability to get goals and assists, both from the number 10 position and left-wing. He also has a great eye for his team-mates in terms of unlocking defences, and I know he will come in and be part of a good team that is already working hard together."
Tottenham Hotspur have made initial contact with Manchester United over a potential move for midfielder Kobbie Mainoo before the transfer window slams shut on September 1, sources have revealed.
The UEFA Champions League draw handed Premier League clubs mixed fortunes, with Chelsea and Liverpool facing tough paths while Tottenham and Arsenal look better placed.
Tottenham Hotspur have ramped up their pursuit of RB Leipzig's Xavi Simons, with the Dutch international now in London for talks that could derail Chelsea's long-standing interest in the versatile attacker.
Tottenham Hotspur have set their sights on Aston Villa's dynamic attacker Morgan Rogers as they race to bolster their squad before the transfer window slams shut on 1 September.
