The deal is worth $53.4 million over six years and includes $22.08 million in guarantees, a league source confirmed to ESPN NFL Insider Adam Schefter.
"I understand they had a lot of confidence in me, a lot of faith in me," Brown said. "I'm just very grateful. I try to put in as much work as possible, and just do my part for this team and make it successful, and I'm going to continue to do that."
The 6-foot-4, 320-pound Brown has started all but four games since the Texans drafted him 26th overall in 2008. Brown earned Associated Press All-Pro second-team honors in 2011 after helping the Texans set a franchise record for yards rushing (2,448).
"We are thrilled to have solidified our offensive line with this extension for Duane," Texans general manager Rick Smith said in a statement. "We believe Duane is an outstanding young left tackle who has the determination, commitment and ability to develop into one of the NFL's top performers.
"It's also an exciting day for our organization. We've laid the foundation for sustained success and this is an important step in building on that and toward a championship."
Houston will break in new, full-time starters on the right side of the line, but Brown has proved to be a durable anchor on the left side, starting all 16 regular-season games in three of his first four seasons. Schaub called Brown the best left tackle in the league before training camp began.
"It's just surreal," Brown said of his new deal. "I've been happy to just make it to this point, to the NFL. But once you get here, it's hard work and I realize that. It took me a while to mature and get to this point in my life where I've become a complete pro and I'm just happy that they recognized that, and had the confidence in me to extend this great deal."
Brown was suspended four games in 2010 for a positive test for a supplement on the league's list of banned substances. He acknowledged then that he made a "naive" mistake and was scared straight by "the longest four weeks of my life."
Offensive line coach John Benton says Brown has shown a new level of maturity and leadership since returning from the suspension.
"We're happy for him," Texans coach Gary Kubiak said. "As a coach in this business, you love seeing players doing it the right way get rewarded. He's been exceptional since the day he walked in the building, not only as a player, but as a person. He's got a lot of bright years ahead of him."
Brown seems to have luck on his side, too, lately. Early in camp, Brown got tangled in a pile and came out limping. An MRI exam showed only a bone bruise in his lower left leg, and Brown was back at practice the following week.
Brown married radio host and MTV personality Devon "Devi Dev" Anjelica in Southern California in July and the two went on a weeklong honeymoon in Thailand. His wife acknowledged him on Twitter soon after news of his contract leaked out.
"Congrats to the man I love (at)DuaneBrown76 on a well deserved new contract," she wrote. "(asterisk)Houston Texas, home of the Texans.(asterisk)"
Information from The Associated Press was used in this report.