Perreault Casgrain, O.C., c.r., (January 18, 1898 – April 26, 1981) was a Canadian lawyer and provincial politician in the Province of Quebec.

[2] Senator Thérèse Casgrain, who campaigned for women's equality and their right to vote, was a distant relative by marriage.

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.

From 1920 to 1936, he was the Crown prosecutor for the Rimouski district, being named King's Counsel ("conseillier du roi") in 1930.

[1] In 1973, he was invested into the Order of Canada, "in recognition of his contribution to the legal profession as well as to the cultural life of the region of Rimouski."