The preliminary agreement for the deal was struck back in April, but complications have delayed the completion.
DiBenedetto's group was set to spend 60 million euros (£52.2m) to own 60% of a company which will own approximately two-thirds of the club, with the rest of the club being owned by Unicredit Bank, who had taken Roma on as part for a debt-for-equity deal with the previous owners, the Sensi family.
Having completed the deal, DiBenedetto is expected to be in attendance for Roma's first fixture of the season, a trip to Slovakia for a Europa League play-off against Slovak Bratislava.
Roma have become the first Italian club to have foreign owners with a controlling stake.
DiBenedetto is a partner in the Fenway Sports Group, who own the Boston Red Sox baseball team and Liverpool Football Club.