The Brazilian defender, unwanted by Manuel Pellegrini, leaves the Etihad Stadium after less than a year at the club and returns to Italy with Rudi Garcia's side.
The Serie A side posted a picture of the defender training with the club on its official Twitter account, alongside the message: "Welcome aboard, Maicon!"
The 31-year-old joined City from Inter Milan in August 2012 for a fee of around 3.5 million euros and made his debut in a 1-1 draw away to Stoke City. He struggled with injuries throughout the season and only made 11 appearances in all competitions for the Blues, though.
New Manchester City boss Manuel Pellegrini revealed that he had no plans to include the right back in his team for the upcoming season, and reports in Italy suggest that City paid the Brazilian 2 million euros to leave.
Maicon established himself as one of the world's leading defenders during his time at Inter, where he scored 16 goals in 176 league appearances.
Maicon and Dutch midfielder Kevin Strootman are the newest signings for Rudi Garcia's Roma, and the newest teammates for USA midfielder Michael Bradley, and could be available to play in the MLS All-Star Game on July 31 at Sporting Park in Kansas City, Kan.