Torino did not wait long to find Sinisa Mihajlovic's successor.
Mazzarri, 56, last managed Watford during the 2016-17 campaign when he secured a second successive top-flight campaign for the Hornets with a 17th-placed finish. The Italian was then relieved of his duties in the summer after one season with the club.
The Torino appointment marks Mazzarri's eighth gig in Italy, including tenures with Sampdoria, Napoli, and Inter. The Tuscan-born gaffer's most successful Serie A spell was with Napoli, which he led to the 2011-12 Coppa Italia title and a runner-up spot in the league the following season.
Torino currently sits 10th in Serie A with 25 points ahead of Saturday's visit from Bologna, five points adrift of sixth place and a coveted Europa League qualifying spot.