The teams announced the deal Sunday.
Perreault has played in 159 games with the Capitals, scoring 70 points with a plus-17 rating. He has won 51.2 percent of his faceoffs.
Perreault began his career in Washington playing for Ducks coach Bruce Boudreau, who also coached Perreault in the AHL.
Mitchell is a left wing who spent last season with the Ducks' AHL affiliate in Norfolk.
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