Ultramontanism in Canada, as in Europe where it began during the French Revolution, was the theory of those who rejected any compromise by Catholicism with modern thought, and demanded the supremacy of religious over civil society. Its central tenet was an attachment to the person of the pope and belief in the doctrine of his infallibility.

Ultramontanism took root in Canada 1820-30, first in the Séminaire de Saint-Hyacinthe, strongly influenced by the ideas of Félicité de Lamennais, and in Montréal under the influence of its first Catholic bishop, Jean-Jacques Lartigue. This bishop opposed Gallican ideas and fought for freedom of the church and for religious supremacy in education. His successor, Mgr Ignace Bourget, led ultramontane ideas to triumph in every field (theology, education, church-state relations, etc) in Montréal and throughout most of Catholic Canada. Ultramontanism, very strong in the 1860s, split into 2 groups. The extreme ultramontanes fought for the immediate application of ultramontane principles in the control of education, the reform of laws in conformity with canon law, and the surveillance of civil legislation by the episcopate, etc. The moderate ultramontanes, whom the extremists called "Catholic liberals," wanted a more prudent application of the principles, with compromise where necessary. The extremists, led first by Mgr Bourget and later by Mgr Louis-François Laflèche, mobilized journalists and conservative politicians, who recommended a programme catholique which would guarantee the supremacy of the church in political life. In following years, the extremists and the "programmists" led an antiliberal crusade, which had, as one consequence, the birth of the Castors in 1882. Despite the belief of ultramontanes in the state, ultramontanism became closely linked with those ideals within French Canadian Nationalism that pointed towards a church-dominated, self-contained society.

Direct intervention by extreme ultramontanists in politics was a failure, but ultramontane thought, with only slight modifications, pervaded philosophic and theological instruction in the petits and grands seminaries, in the social doctrine of the Canadian Catholic Church and in many of the episcopal directives from the second half of the 19th century until the 1950s. It took the Quiet Revolution and the council of Vatican II to dismantle this ideological edifice.