The extension will kick in after next season once Girard plays out the final year of his entry-level contract.
Terms of the deal were not released, but Mike Chambers of the Denver Post reports the contract carries an average annual value of $5 million.
Girard, 21, along with Cale Makar, 20, and Bowen Byram, 18, form one of the most exciting young defence corps in the NHL.
“Samuel has been one of our best all-around defencemen since joining the Avalanche,” said Avalanche general manager Joe Sakic in a press release. “He plays important minutes and is someone our coaches count on to play against other teams’ top lines. He has an exceptional ability to skate and move the puck. As a member of our core, we felt it was important to sign him to a long-term deal and we are excited to announce this extension.”
Last season Girard had four goals and 27 points in 82 games, with nine of his points coming on the power play. He added two assists in nine playoff games.
He averaged 19:54 minutes per game last season, third behind veteran Erik Johnson and the now-traded Tyson Barrie on the Avalanche blue line.
Originally a second-round pick by the Nashville Predators in 2016, Girard was a key piece in the November 2017 trade that sent Matt Duchene to the Ottawa Senators and Kyle Turris to the Predators.