Italian-born Commisso, who also owns U.S. soccer club New York Cosmos and is the chairman and CEO of Mediacom, made a failed offer last year to buy a controlling stake in AC Milan.
Commisso said he had pursued Fiorentina for three years and during that period gained "a tremendous appreciation for how important La Viola is to the city and its loyal fans."
Fiorentina, based in the city of Florence and known as the Viola because of the colour of their jerseys, confirmed they were up for sale earlier this month after fans grew disenchanted with the Della Valle ownership.
Having been re-established in 2002 after going bankrupt, Fiorentina has been controlled by the Della Valle family ever since and has not won any major trophy during that period. The family owns luxury goods group Tod's.
The club narrowly avoided being relegated from the Serie A last month after a difficult season.
(Reporting by Shariq Khan in Bengaluru; Editing by Keith Weir)
