The 24-year-old has put pen to paper on a three-year deal after agreeing personal terms and passing a medical, and is now setting his sights on winning promotion to the Premier League.
Yeates said: "This is massive for me. There was interest from other clubs, but there was only one thing on my mind once my agent told me Middlesbrough had been in touch.
"This club belongs in the Premier League, the fans deserve to be there and I can't wait to play in front of them.
"It's a Premier club in my mind - all you have to do is look around the facilities, the training ground, the stadium, everything is spot-on."
Yeates will link up with his new team-mates when they return for pre-season training next week and begin preparations for what they hope will be a short stay in the Championship.
He told the club's official website: "The gaffer made it very clear how much he wanted me and that was a great feeling.
"He seems absolutely spot-on. He is 110% clear about what he expects of people. He told me that he only wants players who have a hunger. He has certainly has that in me.
"I want to hit the ground running when the new season starts.
"It would me fantastic for me to get back into the Premier League and that's what the gaffer wants to do, that will be the aim this season."
Former Tottenham trainee Yeates, who has been capped at Under-21 level by the Republic of Ireland, scored 12 goals in 42 appearances for League One Colchester last season.
The Dubliner played only four games and made just one start in five years at White Hart Lane, and had loan spells at Brighton, Swindon, Hull and Leicester as well as the U's before making a £100,000 permanent move to the Essex club in July 2007.
He has been touted as a long-term replacement for England winger Stewart Downing, who is currently recovering from foot surgery which seems likely to delay a move away from the Riverside Stadium.
Downing has been avidly pursued by Spurs, who tabled their latest bid for him in January, for several years.
Chairman Steve Gibson persuaded the 24-year-old to stay then, but has promised him he can leave at the right price if a big club comes in for him.
However, the operation he underwent to repair a foot injury within days of the end of last season could sideline him for up to six months in total, and that may mean potential buyers will wait until the winter transfer window to make their move.
Adam Johnson, currently on England Under-21s duty at the European Championships in Sweden, has been cast in the role of Downing's understudy since his emergence from the club's Academy, but he too has been linked with a move away from Teesside this summer after struggling for first-team football in recent seasons.