When the diocese of Québec was created in 1674, the parish church of Notre-Dame-de-l'Immaculée-Conception became a cathedral. About 1740, the growing population of the town was the impetus for a new construction. The Bishop of Québec, Henri-Marie Dubreil de Pontbriand, entrusted this task to Gaspard-Joseph Chaussegros de Léry, the colony's chief royal engineer. He drew up plans to extend the choir, add two side aisles and heighten the nave. The cathedral's reconstruction was complete by 1749.

The Québec Cathedral
Plan, section and elevation of a new cathedral in Québec, by Gaspard-Joseph Chaussegros de Léry, January 4, 1745