The 24-year-old has signed a two-and-a-half year contract and becomes Sean O'Driscoll's first signing as City manager, going straight into the squad for Saturday's npower Championship clash with Ipswich.
Former Forest boss O'Driscoll told City's official website: "He can play right-back, left-back and centre half and is the right age. He has played a lot of games in the Championship and has never let me down.
"Financially, he fits in with what the club want to do in the future and is reliable and solid as a character.
"He has been at a club where he has not had enough games because they have always had the ability to buy someone more expensive. If they sign someone who is more expensive, they usually play ahead of you.
"He's a great character to have around and will fit in really well here at Bristol City."