Anaheim fired Coach Randy Carlyle after Wednesday's 4-1 win over Montreal. That lifted the Ducks' record to 7-13-4, but only Columbus has fewer points in the NHL standings than Anaheim.
Boudreau was let go by the Capitals after Washington, which won its first seven games this season, had lost 8-of-11. He was replaced by former Capitals player Dale Hunter, who lost his debut behind the bench Tuesday.
Boudreau, 56, was in his fifth season coaching the Capitals. He was 201-88-40 at Washington with four playoff appearances.
"We've got a lot of work to do and a hill to climb. This group has faced adversity before and we'll do it again," said Ducks General Manager Bob Murray. "I truly believe this group can do it. I feel we have the gentleman here who can lead us in that direction."
Carlyle had coached the Ducks since the 2005-06 season. He was 273-182-61 and made the playoffs all but one year. Anaheim won the Stanley Cup under Carlyle in 2007.
Boudreau's first game with the Ducks will be Friday against Philadelphia in Anaheim.