The 41-year-old former Italy forward, who led Fiorentina to three successive fourth-placed finishes in Serie A in his three seasons in charge, returns to the club he represented as a player with Sampdoria currently 10th in table.
Montella, who also led Fiorentina to the Coppa Italia final and the semi-final of last season's Europa League, was fired in June after the club announced there had been a breakdown in trust.
"Club president Massimo Ferrero and the whole of Sampdoria Football Club are happy to announce that Vincenzo Montella is officially the new coach," said the club in a statement, adding he had signed a contract until June 2018.
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Montella, spent three seasons as a player at the club from 1996 to 1999 and returned for a further spell on loan in the 2007/08 season.
Sampdoria won their only Serie A title in 1991 with a side which included Roberto Mancini, Gianluca Vialli and Toninho Cerezo.
There have been four other coaching changes in Serie A this season.
Bologna fired Delio Rossi and replaced him with Roberto Donadoni in October, while newcomers Carpi dismissed Fabrizio Castori in September and brought in Giuseppe Sannino, but then reversed the change one month later.
On Tuesday, Palermo fired Giuseppe Iachini and replaced him with Davide Ballardini.
(Writing by Brian Homewood in Berne, editing by Ian Chadband)
