The 20-year-old joins the Championship side as they push for Premier League promotion this season.
Hamilton is an academy graduate and joined City at an under-9 level and was crucial in helping both the club’s Under-18s and Elite Development Squad.
Middlesbrough manager Michael Carrick spoke about the youngster and how excited he is to work with him.
"Micah is an exciting young player who we're looking forward to working with. He's already been in and around the senior side at Man City - he's got that experience from playing in the Champions League - and he is another great addition to the squad."
Hamilton, who is clearly a talented young forward could be just what the side needs to put themselves in to a promotion position this season and find themselves back in the Premier League.