Conte, who was last at Tottenham, has signed a contract until the summer of 2027.
"I am very proud that the new coach for Napoli is Antonio Conte," said president Aurelio De Laurentiis today.
"Antonio is a top coach, a leader. I am sure that the necessary rebuilding can begin with him after the end of the cycle that led us to win the scudetto last year after many seasons at the top of Italian football. Today marks the beginning of an important new chapter in Napoli's history."
Conte replaces Francesco Calzona - who joined as a temporary solution. He will now focus on his job as national team coach of Slovakia.
"Napoli is a place of global importance," Conte declared.
"I am happy and excited about the idea of sitting on the Azzurri bench. I can really promise one thing: I will do my utmost for the growth of the team and the club."
Conte has previously coached clubs such as Inter, Juventus and Chelsea.
The 54-year-old has won Serie A with Inter and Juventus as well as the Premier League with Chelsea.