The Canadiens announced that he will receive a one-year, $2.25 million deal and could earn $1.25 million in bonuses.
After coming up with Montreal in 2003-04, Plekanec played 981 games for the Canadiens before being dealt to Toronto at this past season's trade deadline. The 35-year-old posted two points in 17 regular-season games for Toronto and added four points in seven playoff games.
The two-way center has scored 20 or more goals in a season seven times in his career.
Plekanec had expressed interest in returning to Montreal to register his 1,000th game played. He is coming off a six-year, $30 million contract.