The 22-year-old Empoli star agreed personal terms with Boro earlier this month, but only now have the two clubs finalised payment details over the £8 million transfer fee.
Boro have been linked with a host of new players already during this pre-season, but with manager Steve McClaren away on World Cup duty with England, progress of new signings at The Riverside has remained slow.
Frenchman Franck Queudrue is the only player to have signed permanently since the end of the last Premiership campaign, although Maccarone now seems to be in the bag.
Boro themselves would only say that a deal was nearing conclusion, but the player's agent Paolo Fabbri has told planetfootball.com that the deal is now done.
"Happily, the two clubs have agreed everything over the last two days," Fabbri told planetfootball.com.
"They have signed their agreements and we are very happy.
"Massimo will travel to England on July 7 for a press conference at Middlesbrough and he will begin training on July 8."
Ironically, one of Maccarone's first appearances for Boro should come against his former club, when Middlesbrough travel to Italy in early August for a friendly tournament against Empoli and fellow Serie A newcomers Como.
The Teesside club are now likely to turn their attentions elsewhere in the transfer market, with one target seemingly signed.
Boro are thought to be looking for one more striker, although bolstering of their midfield department would seem to be a more pressing priority with the futures of Paul Ince and Robbie Mustoe still looking far from certain.
The latter is almost certain to leave after only being offered a 12-month contract, while Ince is being strongly tipped to cut his ties with the club.
A renewed bid for Leicester's Muzzy Izzet now looks almost certain, although reports from the North East are suggesting that Ipswich Town's Matt Holland is again coming under McClaren's gaze.
Meanwhile, Croatian ace Alen Boksic has confirmed that he will not be one of those departing the North East club this summer.
"I am staying at Middlesbrough," he said upon his return from the World Cup finals.
"I feel fine there. I didn't expect that I was going to feel like that in England."
