 Born in Lille to a bourgeois family of cloth merchants, Liénart was the second of the four children of Achille Philippe Hyacinthe Liénart and Louise Delesalle.He studied at College Saint-Joseph, the Seminary of Saint-Sulpice in Paris, the "Institut Catholique de Paris", "Collège de Sorbonne", and the Pontifical Biblical Institute in Rome.He was ordained to the priesthood on 29 June 1907, and then taught at the Seminary of Cambrai until 1910, and then at Lille until 1914.