Sarri succeeds Max Allegri in the Allianz Stadium dugout after the former Juve boss announced his decision to leave at the end of 2018/19 after five trophy-laden years.
The 60-year-old joins from Chelsea after ending his lone season in English football on a high note, with the Blues winning the Europa League final in his final match.
They went undefeated throughout their European campaign before beating Arsenal 4-1 in the Baku showpiece to lift the trophy, and reward Sarri with the first ever silverware of his managerial career.
The Blues also finished third in the Premier League and reached the EFL Cup final to make it a solid, if at times shaky, debut campaign for Sarri.
Nonetheless, there was often supporter anger directed at the former Napoli boss over his style of play and team selections, and there were frequent calls for him to be sacked throughout the season.
He leaves Chelsea after Juventus agreed to trigger the release clause in his contract, and has put pen to paper on a three-year deal with the Italian champions.
Frank Lampard, Chelsea’s record goalscorer, is favourite to succeed Sarri at Stamford Bridge though no deal has yet been agreed with Derby to hire the 40-year-old.
Lampard, with former Blues midfielder and youth coach Jody Morris as his assistant, guided Derby to the Championship play-off final in his first season in management, though Aston Villa triumphed in the Wembley showpiece to seal a return to the Premier League.
In a club statement, the Blues confirmed Sarri had asked to leave and an agreement had been reached for the early termination of his contract.
Chelsea director Marina Granovskaia said: “In talks we had following the Europa League final, Maurizio made it clear how strongly he desired to return to his native country, explaining that his reasons for wanting to return to work in Italy were significant.