The former England Under-21 international will cost Birmingham £3million.
The 23-year-old has signed a four-and-a-half-year contract with the Blues.
He told their official website: “I’m over the moon, especially being at the club I supported as a boy.
“I just can’t wait to get out there, put the shirt on and do well for the club. I have not slept properly for the last three or four days waiting until the deal to be done. Now it’s done it’s unbelievable.”
