The club announced Friday it has received international transfer papers for the 35-year-old veteran of more than 200 Serie-A matches in Italy.
Corradi signed a contract with the Major League Soccer expansion team this week.
He will be available for the Impact's first home game against the Chicago Fire on Saturday.
Corradi joined the Impact on a tryout two weeks ago.
A crowd of up to 60,000 is expected at Olympic Stadium for the team's first home game in MLS.