Terms of the deal were disclosed although multiple reports have said the deal with worth $2.2 million.
Thornton, 34, signed with the Bruins as a free agent on July 1, 2007, and has played in 360 regular-season games with Boston, registering 25 goals, 37 assists and 601 penalty minutes while anchoring the fourth line. He has earned the respect of teammates for his toughness and willingness to back them up physically.
This season, Thornton has four goals and eight assists for 12 points and 143 penalty minutes. The 143 penalty minutes are a career high and he leads the NHL with 19 fighting majors.
Thornton, who won a Stanley Cup with the Anaheim Ducks in 2007 in addition to the one he won with the Bruins last season, set career highs in goals, assists and points in 2010-11 with 10-10--20 totals.