After Canadiens starting goaltender Cristobal Huet suffered an injury, Halák was called up on February 15, 2007. During the time of his callup, Halák had recorded a 2.00 goals against average (GAA) with the Bulldogs, which was the lowest in the AHL. He played his first NHL game with the Canadiens on February 18, 2007. He stopped 31 shots and earned a 3–2 road win over the Columbus Blue Jackets. He earned his first career NHL shutout on March 20, 2007. For the shutout, he made thirty saves to keep the rival Boston Bruins off the board with a 1–0 victory. For most of the 2007–08 season, he played for the Bulldogs. After the Canadiens traded Huet, Halák was called up to be the full-time back-up goaltender. His first playoff start was on April 30, 2008 against the Philadelphia Flyers which ended in a 4-2 loss.