كتب : Sherif Tarek
The former Cagliari manager penned a two-year deal to succeed Brazilian tactician Leonardo, who was in charge at San Siro only last season.
The Rossoneri were planning to install Allegri earlier this summer but their negotiations with Cagliari over his contract termination put off the deal.
Under Allegri, Cagliari finished ninth and 12th in the previous couple of seasons.
The 42-year-old was lauded by other Serie A coaches during his tenure at Stadio Sant'Elia. They voted for him to win Panchina d'Oro prize in both Serie A campaigns.
However, Allegri fell out with Cagliari last April after a string of poor results and has been trying to leave ever since.
On the other hand, Milan struggled last term under the guidance of Leonardo, having finished in third spot.
They haven't won the Scudetto since 2004.