He joins Roma after seven seasons at Torino, where he made a total of 251 appearances and scored 113 goals in all competitions.
"Roma's progress and ambition in recent times has been clear for all to see, and both elements have had a big influence on me," Belotti said in a statement on Roma's website.
Belotti has also made 44 appearances and scored 12 goals for Italy and was part of the team who won the European Championship in 2021.
His arrival in Rome follows that in July of Argentina forward Paulo Dybala (28), who also joined Jose Mourinho's side on a free transfer after leaving Serie A rivals Juventus.
Roma are fourth in the table on seven points after three matches and host recently promoted Monza on Tuesday after leaving Turin with a point on Saturday evening against Juventus.
