Boiret came to Canada in 1755 with another priest, Henri-François Gravé de La Rive. His intention was to be part of the mission to the Tamaroa tribe in Illinois but his services were needed at the Séminaire de Québec. There he was to fill a number of offices, including that of bursar and professor of theology. He was appointed a director of the seminary in 1759. This also marked the beginning of the Siege of Quebec. Only Urbain and one other priest, Joseph-André-Mathurin Jacrau, remained at the seminary to manage the affairs of the seminary. However, almost everything was destroyed and Boiret, as bursar of the seminary, moved to Saint-Joachim to take stock of the situation and regroup.