The 24-year-old defender joined City in 2006 and so brings to an end an eight-year association with the Blues for whom he made a total of 36 appearances for, scoring one goal.
Boyata was part of the 2008 City team that won the FA Youth Cup and in 2009/10, he was voted the MCFC Young Player of the Year, but his first-team opportunities have been limited with only eight Premier League starts for the Belgian.
He made his senior debut against Middlesbrough in 2010 and, ironically, his last start for City was also against Boro last January.
His 89th-minute appearance against Spurs last month was his last in sky blue.
Capped once by Belgium, Boyata spent part of the 2011/12 and 2012/13 campaigns with Bolton Wanderers and FC Twente respectively but just 53 senior games and two goals means that his international aspirations have been somewhat curtailed.
On the back of compatriot Jason Denayer's superb season at Parkhead, Boyata will now hope to firmly establish himself with Celtic as well as having the opportunity to play Champions League football next season.
“The manager came to see me in Manchester and I spoke to him about having me here and all the ideas he had for me playing for the team," said Boyata.
“So I was very pleased with his plans and from that point I thought that moving to Celtic would be a good idea and we tried to do everything right for me to move on."
A popular figure among staff and supporters, everybody at City wishes Dedryck the very best for the future.