Julien will take over from Dave Lewis, who was fired by Boston last Friday. The 47-year-old Julien was relieved of his head coaching duties by the New Jersey Devils with three games to go in the regular season. The Devils were 47-24-8 during his time there.
He earlier coached the Montreal Canadiens for parts of three seasons.
Lewis led the Bruins to a 35-41-6 record in his only season. He was fired more than two months after they missed the playoffs for the second consecutive year.
Bruins GM Peter Chiarelli has been on the job only 11 months and has already fired two coaches. Mike Sullivan was let go after Chiarelli took over as part of a major front-office shakeup.
It will be the second time that the Bruins have turned to a Devils coach who was fired by New Jersey in the waning days of the regular season. Robbie Ftorek was fired by New Jersey with eight games left in the 1999-2000 season.