The 23-year-old led Montreal last season with 65 points in 79 games and was second in goal-scoring with 33 goals, two fewer than Erik Cole.
Reports said the deal was worth US$27-million, an average of $4.5 million per season.
He will earn $1.65-million in the final year of his current contract next season. The new deal kicks in for the 2013-14 campaign and runs through 2018-19.
"Thanks for the support everyone! So happy to be a part of this organization long - term.. #habs," Pacioretty wrote on Twitter.
The move was announced Monday night and comes two months after he won the Bill Masterton Trophy for perseverance, determination, and dedication to the game.
The six-foot-two, 210-pound Connecticut native sustained a fractured neck and a concussion in March 2011 after taking a hit from Boston's Zdeno Chara, but returned to Montreal's roster the following season.
He started the Max Pacioretty Foundation to help the Montreal General Hospital Foundation raise money for a Functional MRI machine at the hospital's Traumatic Brain Injury Centre.
Since the Habs drafted Pacioretty 22nd overall in the 2007 draft, he's scored 53 goals and 61 assists for 114 points in 202 career NHL games.