In doing so, they became the sixth NHL team in seven weeks to make a coaching change.
Therrien is the second straight coach of the league's most storied franchise to leave without posting a winning record.
Julien, 42, was in his third season with Hamilton of the American Hockey League. The Bulldogs had a league-best 33-6-3-3 record, and are on pace to break that team's 67-year-old mark for wins and points.
Julien leaves the team in the midst of a 25-game points streak (21
2-2), which is two shy of the league record, and bypasses a chance to coach in the AHL All-Star Game.
The 39-year-old Therrien was named the 25th Canadiens coach on Nov. 20, 2000, and led Montreal to an upset of the top-seeded Boston Bruins in the Eastern Conference quarterfinals last year. The Canadiens had tied a franchise record by missing the playoffs the three previous seasons.
In his brief stint with the club, Therrien compiled a 77-77-13-13 record.
Vezina and Hart Trophy winner Jose Theodore struggled early this season, but improved in December, and Montreal was a season-high four games over .500 (16-12-4-2) on Dec. 21. However, the Canadiens are 2-7-1-2 in their last 12 games, and are tied for ninth in the Eastern Conference.
Therrien replaced Alain Vigneault, who finished with a 109-122-35 record to become the first Canadiens coach without a winning record since Alfred "Pit" Lepine went 10-33-5 in 1939-40.
Montreal is the second team to name a coach this week. On Tuesday, the Atlanta Thrashers named Bob Hartley to replace interim coach and General Manager Don Waddell. Hartley was fired by the Colorado Avalanche on Dec. 18.