The deal reportedly worth US$16.4 million, or $4.1 million per season, takes effect in the 2014-15 campaign. The Russian blue-liner, who has yet to play in 2013-14 due to a knee injury, is earning $2 million this season.
"I love Montreal and I am confident that I will soon return to the ice fully recovered from my injury and contribute to the success of our team," Emelin said in a statement.
The 27-year-old, who was eligible to become an unrestricted free agent next summer, tore an ACL ligament on April 6, depriving Montreal of its most physical defenceman for the final weeks of the 2013 campaign and the playoffs. He is expected back in late November or early December.
"He is an important part of our group of core players," said general manager Marc Bergevin. "He shows a very good work ethic and has a good attitude.
"He can play big minutes against the opponents' best players, and hard-hitting defencemen of his type are hard to find. We are very confident that he will fully recover from his knee injury and be able to compete at a high level for many years to come."
Emelin had three goals and nine assists in 38 games while getting 19:40 of ice time per game last season. The six-foot-two 224-pound Russian, who was drafted in the third round in 2004, has 19 points in 105 career NHL games.