The former Napoli boss has penned a three-year contract at Stamford Bridge.
Sarri, 59, replaces Antonio Conte at Chelsea after the Italian was sacked by the Blues yesterday.
On his new role, Sarri said: “I am very happy to be coming to Chelsea and the Premier League. It is an exciting new period in my career.
“I look forward to starting work and meeting the players on Monday ahead of travelling to Australia, where I will be able to get to know the squad and begin our match action.
“I hope we can provide some entertaining football for our fans, and that we will be competing for trophies at the end of the season, which is what this club deserves.”
Sarri had an impressive three-year spell at Napoli, securing two Serie A second-place finishes, as well as being named the Serie A Coach of the Year in 2017.
Chelsea director Marina Granovskaia added: “We are delighted to welcome Maurizio and are looking forward to him bringing his football philosophy to Chelsea.
“Maurizio’s Napoli side played some of the most exciting football in Europe, impressing with their attacking approach and dynamism, and his coaching methods significantly improved the players at his disposal.
“He has plenty of experience in Serie A and the Champions League and we know he is relishing the chance to work in the Premier League.”
Express Sport revealed last night that Chelsea are looking to complete three deals following Sarri’s arrival.
They have already identified transfer targets and are in talks with Juventus over central defender Daniele Rugani having made a bid of £30m.
The Blues also hope to sign CSKA Moscow midfielder Aleksandr Golovin and Roma goalkeeper Alisson.
Chelsea are also expected to sign former Napoli midfielder Jorginho, who underwent his medical this week.
The Blues now face a tough legal battle with former Italy boss Conte.
When Conte was axed by chairman Bruce Buck, according to sources in Italy, he was told he would receive no lump sum due to “a series of irregular behaviours”.
His controversial dumping of Diego Costa via text last summer is thought to be the key issue, with the club claiming that action reduced the value of the player.