The Impact announced Thursday that they had signed the veteran Italian forward, who became the Major League Soccer expansion team's first designated player.
Di Vaio, who cost Juventus 14 million euros (C$18 million) a decade ago, will be available to play once the transfer window officially opens June 27.
"We thought it was a longshot and today we're very proud of this moment because he is one of the players that we wanted from day one," Impact sporting director Nick De Santis said Thursday.
De Santis spoke as renovation and expansion work at Saputo Stadium continued behind him with Di Vaio's No. 9 displayed on a section of the stadium's seats.
"With Marco we're getting someone that has a strong character, that has a strong will to help this club move forward."
The 35-year-old former Italian international agreed to an 18-month contract with the Impact, who have a pair of one-year options to extend the deal.
Di Vaio has 142 goals in 342 games in Serie A, with Lazio, Bari, Salernitana, Parma, Juventus, Genoa and, for the last four seasons, in Bologna, where he led the club with 10 goals and seven assists in 37 matches this season.
"First and foremost a player needs to feel important and we did everything we could to make him feel that this was one of the most important acquisitions," said De Santis, who met Di Vaio in Italy in February.
"If we could go back to two years ago when we started envisioning what type of players and, especially as a goal scorer, who we'd want to go after, he was — I can swear to you — the first one on my mind."
In the statement announcing the signing De Santis referred to Di Vaio as Bologna's "catalyst" in avoiding relegation from the top Italian league.
"It was not an easy choice to leave Bologna but I hope to be able to serve a similar role in Montreal, as I am prepared to give everything I have, including my experience and leadership for my coaches, my teammates and the organization," Di Vaio said in a statement.
Designated player means only a portion of his pay is applied to the team salary cap. A DP over the age of 23 counts as US$350,000 against the club's salary budget, unless the player joins his club in the middle of the season, as with Di Vaio, in which case his budget charge is only $175,000.
"It was important that we get a designated player and we've always said we needed to take our time and do our due dilligence in bringing a player that basically filled all the aspects we were looking for, not only a good player on the field but all the responsibilities that come with the designated player," De Santis said.
The Italian is slated to arrive in Montreal with his family on Sunday.
"He feels that it will be an environment where he can adapt a lot easier than going somewhere else just because of who we are and what we've built," De Santis said.
Di Vaio also played for Valencia in Spain, AS Monaco in the French league, and Italy's Verona.
"We know he will bring a great element of attacking presence to our team," said Impact head coach Jesse Marsch. "His nose for attacking plays and ability to score goals will make us a better team."
The five-foot-11, 172-pounder scored two goals in 14 games for the Italian national team and was a part of Italy's Euro 2004 squad, which included the Impact's Bernardo Corradi and Matteo Ferrari.
Montreal (3-6-3) could use a striker this season. The Impact are 12th in the MLS with 13 goals so far, and have 18 against.
Corradi, who leads Montreal with four goals, signed a three-month deal with Montreal on March 15. The Impact has until June 30 to decide whether they'll keep the Italian striker.
"We've sat down with him and said that our intentions are to go forward with him," De Santis said. "We'll see. He's shown great interest in staying. He's excited about what we're trying to do here. He finds a great environment around the team.
"I think the coaching staff has done a great job to bring different players from different parts of the world together and these are things that they appreciated very much, so hopefully we can come to an agreement with Corradi as well."
Note to readers: This is a corrected story. A previous version stated Montreal had 18 goals this season instead of 13.Suggest a correction