Mitchell was acquired in a trade with the Sabres earlier this year.
The deal is worth $3.6 million, according to ESPN's Pierre LeBrun.
The Canadiens acquired Mitchell in a trade with the Sabres in March. The seven-year pro recorded 14 points, including six goals, last season in 51 games for Buffalo and 14 games for Montreal. Mitchell also tallied five points in 12 playoff games for the Habs.
The Canadiens finished this season with 110 points, good for first place in the Eastern Conference's Atlantic Division. Montreal fell to Tampa Bay in the second round of the Stanley Cup Playoffs.
- Stanley Kay