Despite the addition of fortifications at Montreal, the city became a British colony after New France was lost in 1763 with Britain’s victory in the French and Indian War. No visible impact of this transfer would be seen until the end of the eighteenth century, as construction methods employed during the French regime continued. The religious character of the city would however change as the Catholic clergy distrusted the British authorities and their Protestant beliefs, choosing to instead leave and join smaller communities throughout the outlaying area after a massive fire on June 6, 1803 destroyed not only the prison, and dozens of homes, but also the church, and many dependencies of the remaining Jesuits. A third of these properties were in turn gifted to the colony by the two speculators that purchased the land, resulting in the old church of the Jesuits being turned into Place Vauquelin, and Montreal City Hall being erected on the old Jesuits gardens. Fires such as these would continue to wreck destruction upon the colony over the first half of the nineteenth century, and would even take the Parliament building in 1849, resulting in the Parliament being moved to the new capital of Ottawa. Throughout all of this the colonial authorities took advantage of the devastation, tearing out the old fortifications surrounding the heart of Montreal to enlarge not only the perimeter, where rich merchants could build their luxury residences, but to improve access to the growing suburban communities.

Through these transformations an emerging bourgeoisie merchant class began to flourish as port activity grew. Old Montreal as a result became less residential and more geared to the financing and banking of these activities. St. James Street for example became the financial center as it instead became home to large banks, insurance companies, and the stock exchange. Which resulted in a shift in the appearance and tone of the city as predominately Anglophone architects were brought in to design not only these places of business, but institutional buildings such as the Old Court House; even the Notre-Dame Basilica’s façade is the work of James O’Donnell, an Irish Protestant from New York.