The Serbian spent seven years at the Etihad Stadium, a period that saw the Club win two Premier League titles, an FA Cup and two League Cups.
He will now join up with the Italian side in Boston on their pre-season tour of the USA and begin the next chapter of his career.
“When I came in 2010, honestly, I didn’t expect to play so long,” Kolarov told mancity.com. “Today is the day I have to say goodbye. Everything was quick the last couple of days. For me, it’s a very sad day.
“In every part of the Club we have improved not 100 per cent but 200 per cent. Now we are a far better Club than what we were when I came. I am proud that I was part of making City the Club that it is.
“For me it was a great pleasure to play for this shirt.”
He joined City from Lazio in 2010 and by the end of his first season the Club’s 35-year wait for major silverware was over after victory over Stoke in the FA Cup final at Wembley.
The following year saw City win their first league title for 44 years with a last-day win over QPR snatching the title from the grasp of cross-town rivals Manchester United in dramatic circumstances.
In 2013/14, City won a league-and-cup double. They beat Sunderland in the final of the League Cup in February, with Kolarov playing the full 90 minutes at Wembley, before securing their second title in three years with a win over West Ham on the last day of the season. Kolarov played 44 matches in all competitions throughout a campaign that saw the Blues score a remarkable 156 goals.
Another League Cup followed with victory over Liverpool in the 2016 final, before City made it to the semi-final of the Champions League for the first time later that year.
Last season, he operated as a centre-half on several occasions, demonstrating his versatility and ability to play in a number of different systems.
In total, he made 244 appearances for the Club.
Everyone at Manchester City would like to thank Aleks for his contribution to City’s recent success and wish him well with his move to Roma.