The former France international has cost the Giallorossi £2.15million with add-ons subject to the club qualifying for the Champions League.
Roma Sign Newcastle Target
Tottenham, Newcastle and Manchester City had been linked with the former Monaco captain this summer.
Giuly: "I am happy to be at Roma. I have so many important memories with Barcelona but now I am here to win."
Giuly joined Barca from Monaco in 2004 and proved to be a pivotal acquisition as the Catalan giants won two Primera Liga titles and the Champions League during his three-year stay.
Giuly is Roma's second major summer signing following the arrival of Brazilian defender Juan from Bayer Leverkusen.