Miller will now remain at the franchise until the end of the 2015 season with the final year worth a reported £5.9m to the player, who is looking forward to recovering from injury.
"You want to just wake up and push through it, but it's not one of those things," Miller told the club's official website.
"You've just got to be patient and grind and let your body heal. Everybody's body is different. It just depends on how your body is reacting to the rehab. It's just something that you can't rush. You've got to take your time with it."
Miller played nine games for the Broncos last season before his injury.