Born in Laval, Quebec, Played played with the Richelieu Riverains in the Quebec Midget AAA Hockey Leauge. In 1992-93, he joined the QMJHL's St-Jean Lynx and played there for parts of three years. He was selected 44th overall by the Montreal Canadiens at the 1994 NHL Entry Draft then spent the better part of the 1994-95 season with the Hull Olympiques. During the 1994-95 season, he led the league 32 wins and helped his club reach the Memorial Cup tournament. A member of Canada's Gold Medal World Junior team in 1996 and the tournament's Top Goaltender, Theodore split his first four professional seasons with Montreal and Fredericton of the AHL. He made 30 appearances in 1999-00 and recorded five shutouts with an impressive 2.10 goals against average and was a member of Canada's World Championship team where he was named to the Second All-Star Team. During the 2000-01 season, Theodore became a workhorse for the Canadiens after a season-ending injury to Jeff Hackett and became the team's number one netminder the following year. The 2001-02 season was a dream season for the Laval, QC native leading the Habs to their first playoff appearance in four years and capturing numerous awards including the George Vezina Trophy as Top Goaltender and the Hart Memorial Trophy as Most Valuable Player. Coming off a career year in 2001-02, Theodore and the Canadiens struggled the in 2002-03, missing the post season, yet rebounbing in 2003-04 with a career high 33 wins, and was subsequently named to Canada's entry in the 2004 World Cup of Hockey.