The restricted free agent signed a US$5-million, two-year deal on Wednesday, agreeing to terms less than 48 hours before NHL players will report for medicals.
Marchand earned a raise on the $600,000 he made as part of his entry-level deal last year.
The 23-year-old is coming off his first full season in the NHL and was a big contributor to Boston's Stanley Cup victory over Vancouver.
The agitator had five goals during the championship series, including two during a 4-0 win in Game 7.
In 77 regular-season games last year, Marchand had 21 goals and 41 points.