The 67-year-old replaces Raffaele Palladino, who was dismissed last week despite guiding Atalanta to a seventh-place finish in Serie A and qualification for next season's Conference League.
According to the club's official statement, Sarri has signed a three-year contract worth around €3 million per season plus bonuses.
Sarri brings a remarkable managerial record to his new role, having taken charge of more than 800 professional matches across a career that began in the amateur leagues around Arezzo.
His trophy cabinet includes the UEFA Europa League with Chelsea and the Serie A title with Juventus, along with individual honours including the Panchina d'Oro for the 2015-16 season.
"The Percassi family, the Pagliuca family and everyone at Atalanta extend a warm welcome to Maurizio Sarri and his staff to the Nerazzurri family," the club said in its statement.
Born in Naples but raised mostly in Tuscany, with a brief childhood spell in the Bergamo area, Sarri's path to the top of European football was a gradual one.
He guided Sansovino from the regional Eccellenza division to Serie C2 in three years, before taking Empoli back into Serie A in 2014 and securing their survival the following season.
That work earned him the move to Napoli in the summer of 2015, where he formed a productive partnership with sporting director Cristiano Giuntoli, the same man who now occupies that role at Atalanta.
Sarri broke Napoli's points record in three consecutive seasons at the club, reaching a tally of 91 points in 2017-18 that remains the club's record to this day, while securing Champions League qualification with two second-place finishes and a third.
International recognition followed during his time at Chelsea, where he won the Europa League in 2019 with a final victory over Arsenal in an all-English showpiece.
He added the Serie A title with Juventus the following season.
Most recently, Sarri spent time across two spells at Lazio, where he led the club to a second-place Serie A finish in 2022-23 and a Champions League last-16 appearance in 2023-24, the club's second-best ever result in Europe's top competition.
His final season in Rome proved more difficult, with Lazio finishing ninth in Serie A and losing the Coppa Italia final to Inter Milan, before the two parties agreed to terminate his contract early.
Sarri becomes Atalanta's third permanent head coach since Gian Piero Gasperini's departure last year, a reflection of the instability the club hopes his experience can finally bring to an end.
With Conference League football on the agenda and a sporting director who already knows his methods intimately, Atalanta's bet is that Sarri's identity-driven football can deliver the same kind of consistency he found during his best years in Naples.