Sky Blues boss Peter Reid has been active in the transfer market over the summer and has now added Carey to his squad.
Carey rejected two contract offers to stay at Ashton Gate and has opted for a two-year deal with the Championship outfit.
The 27-year-old had spent his entire career with The Robins but has decided to grasp the opportunity to step up a level.
Reid is confident the full back will prove to be a valuable addition to his Highfield Road squad over the next two seasons.
"I've known the boy for a long time and he's a very experienced player but still quite young in relative terms," Reid told the club's official website.
"He's played at this level before when Bristol City were in Division One and I remember him coming to Sunderland and he stood out then.
"He's predominantly a right back but he can just as easily slip in to the centre and I think he will do a really good job for us."
