The 29-year-old Spain international spent the second half of last season on loan at the Serie A club.
Llorente made 59 appearances for Leeds after signing for a reported £18m in 2020.
He was loaned to Roma in January and he impressed manager Jose Mourinho in his 12 appearances.
He won a Europa League runners-up medal after appearing as a substitute in Roma's penalty shootout defeat by Sevilla in May's final.
Llorente has 10 caps for Spain and is under contract at Elland Road until 2026.