Cole, who was a free agent after his contract at Chelsea expired, arrived in Italy's capital on Monday to seal the switch.
A statement on the club's website confirming the news read: "AS Roma SpA announces that it has signed a contract with the English footballer Ashley Cole, lasting two years, expiring on 30 June 2016."
The deal includes an option to extend for a further 12 months.
A veteran of 107 caps, the left-back announced his retirement from international football in May after missing out on a place in England's squad for the FIFA World Cup in Brazil.
He claimed eight major honours during his time at Chelsea - including the 2011-12 UEFA Champions League - but fell out of favour under Jose Mourinho last season, making just 15 Premier League starts
