Tonali has joined Spurs in a £100m deal that sees the London club pay an initial fee of £92.5m, with a further £7.5m of add-ons also included as part of the final package.
The fee is the second-highest Newcastle have ever received for selling one of their players, behind only the £125m agreement that took Alexander Isak to Liverpool last summer.
Having joined Newcastle from AC Milan in the summer of 2023, Tonali leaves Tyneside having made 110 senior appearances for the Magpies, scoring ten goals.
He was part of the team that won the Carabao Cup in March 2025, and also played a prominent role in Newcastle’s two Champions League campaigns during his time in the North-East.
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However, his spell at St James’ Park was blighted by the ten-month ban for gambling offences that occurred during his time in Italy, but which was served while he was a Newcastle player, with the club and its fans standing by him throughout his suspension.
Posting on his Instagram, Tonali said: "Three years ago I came to Newcastle not really knowing what to expect. Today it’s time to say goodbye and it’s hard to find the right words.
“Above all, I want to speak directly to the fans. When things were hard for me, you were there. Not for one day did I feel alone. I felt it every time I was at St James’ Park. That’s something I will carry with me for the rest of my life.”
Spurs' club-record signing of Tonali continues a remarkable summer spending spree that has seen the north London club spend £85m on Mateus Fernandes in a deal that was announced on Thursday and £52m to bring Jan Paul van Hecke from Brighton, taking their total spending to £237m. Martin Dubravka, Andy Robertson and Marcos Senesi have also signed as free agents,
"I'm very happy to be here," said Tonali, on Spurs' official website after his move was confirmed. "When I arrived at the club today, it felt fantastic. People said about there being four or five clubs - there was only one.
"I spoke to the head coach for close to two hours about the club, the fans, the stadium and our football. It was like magic because I knew immediately that I had to sign for Tottenham. I've played against Tottenham a few times and always found a great atmosphere made by great fans. I can't wait to start the season."
Roberto de Zerbi's presence in the Tottenham dugout was a major factor in Tonali choosing to join a club that finished a lowly 17th in the Premier League table last season.
"Sandro is a special player and a great signing for our club," said the Spurs boss. "I have followed him for a long time, as he came through the youth system at my hometown club, Brescia, and I'm so happy to be working with him now.
"Given his qualities, there was a lot of interest in Sandro this summer. However, he was very clear in his desire to join Tottenham, and I know our fans will love what he brings to the team."