O'Brien, 27, appeared in 80 games for the Nashville Predators this past season, scoring 2 goals and finishing with 9 points, along with 83 penalty minutes. The Port Hope, Ont., native had no points in 12 playoff games for Nashville.
"We are pleased to have Shane under contract," Avalanche General Manager and Executive Vice President Greg Sherman said in a statement. "He adds depth and brings an element to our defense."
Selected by Anaheim in the eighth round (No. 250) of the 2003 Entry Draft, O'Brien has appeared in 379 career NHL games with Anaheim, Tampa Bay, Vancouver and Nashville. He has 10 goals and 64 points, along with 688 penalty minutes. He has also skated in 40 career playoff games, recording 2 goals and 3 assists.