The 23-year-old has agreed an initial contract which runs until 2028.
The 23-year-old Italian midfielder has signed an initial deal that will keep him at St James’ Park until 2028 for an undisclosed fee – believed to be in excess of £50m.
Tonali, who has 14 senior caps, has captained his country at the European Under-21 Championship in Georgia and Romania in recent weeks and the announcement of his signing came a day after the Italians exited the competition.
The former Brescia player said: “First of all I want to thank Newcastle United because they are giving me a huge opportunity for my career.
“I want to repay the trust on the pitch and give everything, as always. I’m really excited to play at St James Park, I can’t wait to feel the warmth of the fans.”
Tonali is the type Magpies head coach Eddie Howe has targeted since guiding the club to a top-four finish in the Premier League last season to end a two-decade exile from Europe’s most prestigious club competition.
Howe has signaled his intention to recruit quality over quantity this summer while staying within the spending limits under which the club must operate, having invested more than £250m in the first three transfer windows under its new Saudi-backed owners.
He admitted it will be difficult to compete on the domestic and European fronts next season and knows repeating a remarkable league campaign will be made all the more difficult by having to face the continent’s big boys again.
However, signing a player of Tonali’s stature is a sign of the direction Newcastle want to take and the 45-year-old was delighted to land his man.
Howe said: “I am delighted to welcome Sandro to Newcastle United. He is an exceptional talent and has the mental, physical and technical attributes to make him a great fit for us.
“At 23, Sandro already has important experience as a key player in one of Europe’s top leagues and in the Champions League, as well as playing for his country.
“But he also has the opportunity and potential to grow and develop with us and I’m excited to add him to our squad as we head into an exciting season.”
Tonali began his career at Brescia, where he helped the club win promotion to Serie A, and moved to Milan in the summer of 2020, initially on a long-term loan deal.
He left with 130 appearances in Italy’s top flight and played in all 12 of the Rossoneri’s Champions League games last season as they reached the semi-finals where they were beaten by arch-rivals Inter.