Zappacosta emerged as a late transfer target for Chelsea on deadline day, with the Premier League champions understood to have agreed a £21m deal for the Italy international.
A statement on the Torino club website confirmed that the move will go ahead despite not being revealed before the 11pm transfer deadline, while Chelsea also announced the deal later in the evening.
“It is a dream for me to join Chelsea and play in the Premier League. I am very excited to be here and start working with the team. I hope I can show my quality to the coach, my teammates and the supporters,” Zappacosta told the club’s official website.
The 25-year-old, who was handed the first of his four Italy caps during Antonio Conte’s time in charge of the national team, could make his debut for the Premier League champions against Leicester City after the international break.