The former Italy manager had a year remaining on his current contract and had already taken charge of pre-season preparations at the club's Cobham training ground outside London.
The Italian boss was finally confirmed as the club's new manager on Saturday after the Blues parted company with Antonio Conte last week.
Conte's been absent from all social media posts by the club, which has only fuelled rumours that he won't be in charge by the time the Premier League season starts in August.
And Sarri has revealed his happiness at signing for Chelsea FC after months of speculation linking him with the Stamford Bridge job.
Playmaker Cesc Fabregas "liked" a message welcoming Conte's departure on Twitter, later apologising and suggesting he had pressed the button in error.
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Conte won the 2016-17 Premier League title with Chelsea in his first season as head coach and signed an improved contract, but not an extension to the deal which was due to expire in June 2019.
Conte's relationship with Chelsea's hierarchy was strained after disagreements over their transfer policy last season.
Sarri has replaced Conte as boss before, with a short-lived spell at Arezzo in 2006-07 before Conte was reappointed.
This is arguably the toughest period of Abramovich's ownership, with the Russian facing visa issues with the United Kingdom authorities.
Italy midfielder Jorginho has followed Maurizio Sarri to Chelsea from Napoli.
Chelsea believe they have got in Sarri an astute tactician who produces sides playing exciting football with his three years at Napoli harvesting two second-placed finishes in Serie A.