He was born at Detroit in 1852, the son of Charles Eusèbe Casgrain, and studied at the Petit Séminaire de Québec and the Université Laval.
Although the crown was represented by a large team including George Burbidge, Christopher Robinson, Britton Bath Osler and others, Casgrain was the only French-Canadian in the group.
Pro-Riel sentiment in the province of Quebec was so strong that he was burned in effigy during at least one demonstration.
He represented Montmorency as a Conservative Member of Parliament in the House of Commons of Canada from 1896 to 1904 and Quebec County from 1914 until his death from pneumonia at Ottawa in 1916.
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