Former Blues boss Barry Fry completed the signing of the former Sheffield Utd player on Tuesday evening just hours after he lost a tribunal case in which he contested the termination of his contract at St. Andrew's.
"I am delighted to sign Curtis as he is a quality player who was once a £1 million player and the beauty of it is he is still just 23-years old. He is a fantastic addition to our squad and it is great we have secured him for three years," Fry told the Posh official website.
"He needs a few games under his belt because he hasn't played that much football in recent times, but we know what he is capable of and it is great that we have him on board. We have now received all of the clearances from the Football League and he is ready to help Posh move up the table."
"As a young lad he was a very highly rated player and he commanded a big fee. He played for the England under 21 side and I think it is the first time Posh have signed a £1 million player."