Clark will earn $1.5 million this season in the final year of his old deal and then make $3.5 million in each of the 2008-09 and 2009-10 seasons. The 30-year-old had a career-high 39 points (10-29) in 82 games last season. His 23:40 average ice-time per game led the Avalanche.
"Brett has been an instrumental part of our team's overall success," Avalanche GM Francois Giguere said in a statement. "He's been a steady, dependable asset to our defensive group and we expect him to be a strong contributor to this club in the coming seasons.
"Brett's shown a tremendous amount of perseverance and he's demonstrated his commitment and dedication to our organization."