Braun, 27, established career highs last season for points (17), goals (four) and assists (13). He also finished second on the team in average ice time at 20 minutes 59 seconds per game.
"Justin has emerged as one of our most well-rounded and dependable defencemen," Sharks general manager Doug Wilson said in a statement released by the NHL club. "He's an excellent skater who excels in matching up against the opponents top players on a nightly basis and fits in well with our core group of younger players.
“We feel Justin has just scratched the surface of his talent and we are excited to have him under contract for the next six seasons."
Braun’s extension will begin at the start of the 2015-16. He will make $1.25 million US this season.
Braun’s career season in 2013-14 also saw him become one of four Sharks to play all 82 regular-season games. The Minneapolis native tied a franchise record with eight blocked shots on Nov. 29 vs. St. Louis, and he posted two points in seven playoff games.
In 217 NHL regular-season NHL contests, all with San Jose, Braun has collected 46 points on eight goals and 38 assists.
Braun, who played for the United States at the 2012 world hockey championship, was drafted in the seventh round (201st overall) by San Jose in 2007.