Perreault Casgrain, O.C., c.r., (January 18, 1898 – April 26, 1981) was a Canadian lawyer and provincial politician in the Province of Quebec. He served one term as the national President of the Canadian Bar Association. Casgrain was educated at a boarding school, Saint-Jean-Berchmans at Québec, at the Séminaire de Québec, at St. Procopius College (now the Benedictine University) in Chicago, Illinois, at the Collège de Sainte-Anne-de-la-Pocatière and at the Université Laval. He volunteered for the Canadian Army during World War I, as an officer in the 1st Canadian Tank Battalion.