Boudreau replaces Randy Carlyle, who was fired shortly after Wednesday's victory over the Canadiens, which improved the club's record to 7-13-4.
Carlyle had been the Ducks' head coach since 2005-06 and led them to their first Stanley Cup title the following season, but they missed the playoffs the last two years.
The Ducks went 273-182-61 during Carlyle's tenure.
Also let go were assistant coaches Dave Farrish and Mike Foligno, and video coordinator Joe Trotta, setting the stage for a new regime under Boudreau.
Boudreau had guided Washington to first-place finishes in the Southeast Division in each of the past four years after taking over behind the bench on November 22, 2007. However, the talent-laden team never advanced past the second round of the playoffs and was off to a middling start this season (12-9-1) before Boudreau was let go on Monday.
"This was an extremely difficult decision," said Ducks executive vice president/general manager Bob Murray. "Randy is a terrific head coach, and did a tremendous job for us for six-plus seasons. ... At this time, we simply felt a new voice was needed. Bruce is a proven winner with a great track record, and we are optimistic we can turn this season around under his leadership."
Boudreau had a record of 201-88-40 in the regular season and reached the 200- win plateau faster than any coach in modern NHL history, but the team managed only a 17-20 mark in the playoffs.
Brad Lauer was also added to the Ducks' staff as an assistant coach.