"He has Champions League experience and has played a decent amount of Premier League games as well," Rovers boss Mark Hughes told the club's official website.
"He is naturally left-footed which gives us balance on the left side which we didn't have with Lucas Neill."
"I just like his attitude to the game. He wants to get up to people, to put pressure on people and really he just fits the bill as far as I'm concerned.
"Liverpool really appreciated the qualities that he has and they weren't too keen on allowing a good young English player to leave their football club.
"I think that is the reason maybe the deal hasn't been done before."