The eight-year deal is the longest allowed under the current collective bargaining agreement for a team re-signing its own player.
Rask compiled a 19-10-5 record last season, with a goals-against average of 2.00, a .929 save percentage and five shutouts.
He went on to post a 1.88 GAA .940 save percentage in 22 playoff games as the Bruins advanced to the Stanley Cup final, losing to Chicago in six games.
The six-foot-three, 185-pound native of Tampere, Finland was drafted in the first round, 21st overall, by Toronto in the 2005 draft. The Bruins acquired Rask from the Maple Leafs in exchange for Andrew Raycroft on June, 24 2006.