Kolarov joins AS Roma on a permanent transfer for a fee of €5 million.
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.
The 31-year-old has signed a three-year contract that runs until 30 June 2020.
The left back 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.