Boston signed the 24-year-old forward to an US$18-million, four-year deal that pays $4.5 million per season.
Marchand, a key part of the Bruins' Stanley Cup championship in 2011, had 28 goals and 27 assists last season.
He also had a plus-31 rating that was fifth overall in the NHL.
The five-foot-nine, 183-pound Halifax native was drafted 71st overall in the 2006 draft and has 49 goals and 48 assists in 173 career games.
The deal comes as the NHL and NHLPA prepare for a potential lockout ahead of the Sept. 15 deadline for the current collective bargaining agreement.