The 21-year-old, who put pen to paper on a new two-year deal last summer, will now stay with the Robins until at least the summer of 2019.
Manager Steve Cotterill told the club’s official website: “Joe was another player we were keen to get signed up to a longer contract and I’m pleased we’ve been able to do that now.
“Joe fully deserves this extended contract for the season he’s had. He’s an intelligent, down-to-earth lad who clearly has his head screwed on.
“Last summer he spoke about the importance of the 2014/15 campaign and he took his chance. Now he’s got to do it again in the Championship and perform to his best.
“It’s good for the football club to have our younger players tied down and pleasing for the lads as well.
“It probably won’t stop at Joe, but his is one, along with Marlon (Pack) and Aden (Flint), that we’ve been able to fit in early in the summer.”
Bryan made the left wing-back position his own last season and made a total of 50 appearances, scoring seven goals.