The 26-year-old, who most recently joined from Premier League rivals Newcastle, says the decision was easy.
"I spoke to the coach about the club, the fans, the stadium and football for almost two hours... It was magical. I knew immediately that I had to sign," says Tonali.
Coach Roberto De Zerbi:
"I've been following him for a long time, as he comes from his hometown club Brescia. I'm so happy to be working with him."
Tonali will therefore become clubmates with the Swedish duo Lucas Bergvall and Dejan Kulusevski.
