The Major League Soccer expansion team signed 35-year-old Corradi after he trained with the team for two weeks on a try-out. Terms of the deal were not released.
He can't play until his international transfer papers come in and he may also need to continue work on his fitness, so he is unlikely to see action in the club's first MLS home game Saturday afternoon against Chicago.
Corradi scored 68 goals in more than 250 games in Serie A, including time with Chievo Verona, Lazio, and most recently Udinese. He has won a European Super Cup and an Italian Cup.
"I had a feeling early on that it would be a good fit for both sides," Corradi said in a statement. "Now, I will do my best to help the team reach the level that this club and this city deserve."
He was recommended to the Impact by defender Matteo Ferrari, who joined the club earlier. The two knew each other from playing on the Italian national squad and had been training together with a third division club in Italy.
When Ferrari joined the Impact, he contacted Corradi to say the team may need a proven striker.
"He has a lot of experience," Ferrari said this week. "He played on great teams in his career, so he knows his timing, how to move in the ground, he's strong and he can score, make assists.
"I don't want to speak only of Corradi because I called him. There are other players here. It was an opportunity. I was sure he would be super-enthusiastic to come. When he's ready, he'll be important for us."
Scoring goals is expected to be a challenge for the Impact, who made failed attempts to sign a handful of well-known older European stars like David Trezeguet and Alessandro Del Piero as designated players, or those paid more than the league's salary limit.
And their first pick in the expansion draft, veteran striker Brian Ching, was unhappy and was dealt back to the Houston Dynamo.
Sanna Nyassi and Justin Braun were ineffective as the starting forwards in the Impact's first MLS match in Vancouver, a 2-0 defeat.
Corradi played in the Impact’s final game of the pre-season, a 1-0 win March 3 against Swedish first division side BK Hacken, assisting on the game’s only goal.
Impact coach Jesse Marsch said Corradi is "a good player, a good leader and has great experience."
Corradi also played in Spain with Valencia and in England with Manchester City. He has 13 caps for Italy.