The England goalkeeper will play in Serie A for the coming campaign, having been replaced by Claudio Bravo at the Etihad Stadium
The England international goalkeeper found himself second choice behind Willy Caballero for City's opening games of 2016-17, with Claudio Bravo's arrival from Barcelona seemingly demoting Hart to third choice.
Hart arrived in Turin on Tuesday, with the loan moved confirmed on transfer deadline day.
He was made captain for City's Champions League play-off game against Steaua Bucharest last week and bade an emotional farewell to the club's supporters.
The 29-year-old will now have a chance to prove himself again after a pair of high-profile errors on international duty with England at Euro 2016.
England and Hart, capped 63 times for his country, face Slovakia in a World Cup qualifier on Sunday in what will be Sam Allardyce's first match in charge of the national team.
Hart could then make his Serie A debut for Torino at Atalanta on September 11.
He joined City in 2006 and has made 348 appearances for the club, with his honours including the 2011 FA Cup and Premier League titles in 2011-12 and 2013-14.