The Tuscan club has been looking for a coach since parting company with Delio Rossi towards the end of last season.
A statement from Fiorentina read: "ACF Fiorentina announces that Vincenzo Montella is the new coach of the first team.
"Montella has signed a two-year contract with an optional third."
Montella, 38, parted company with Catania earlier this month after guiding the Sicilian outfit to an 11th-placed finish in Serie A in his first season in charge.
The former Roma boss had one year left on his contract with Catania but was granted an early release from his role.
Fiorentina ended the season two places and two points behind Catania.
Montella will be introduced to the media on Monday afternoon.
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