The goalkeeper has put pen to paper on a two-and-a-half-year deal that will keep him with the Chairboys until June 2013.
Bull, who is a fans favourite at Adams Park, was over the moon to sign a new deal.
"I'm delighted. I've never enjoyed my football more than I am now. I've got a great relationship with the manager, players and the fans, and it was a no-brainer," he told the club's official website.
Manager Gary Waddock was pleased to keep hold of his prized asset.
"Bully has played at a consistently high level this season but I didn't expect anything else. I'm absolutely delighted that he has committed himself to the club. We are trying to build something here and he plays a big part in our plans for the future," he added.