The 20-year-old Seguin, who was drafted second overall by Boston in the 2010 NHL Draft, set career highs last season in goals (29), assists (38) and points (67) for a Bruins team that won a second consecutive Northeast division title.
The All-Star forward's contract averages $5.74 annually and extends through the 2018-19 NHL season, the Bruins said in a statement.
Seguin was part of Boston's Stanley Cup-winning squad in his 2010-11 rookie season. In the 2011-12 NHL campaign he became the youngest player to lead the Bruins in scoring while also posting a plus-34 rating that was second in the league only to team mate Patrice Bergeron.
