Thérèse's father, Sir Rodolphe, had represented the Charlevoix riding since the general election of 1904, holding it as a Conservative. However, he was opposed to conscription and with the Conscription Crisis looming, he decided that he would not stand for re-election in the general election of 1917. Her husband, Pierre Casgrain, sought the nomination in the new Charlevoix—Montmorency riding for the Liberal Party as a Laurier Liberal, opposed to conscription. He was elected in the general election.