He became a very successful merchant and was heavily involved in the Montreal end of the fur trade. His brother, Jean-Louis, was heavily involved in the fur trade and exploration and Luc controlled the eastern end of his activities. Another brother, François-Josué de La Corne was the commandant of Fort Kaministiquia for a time and large fur trade profits were realized. He was in partnership with Louis-Joseph Gaultier de La Vérendrye for three years south of Lake Superior. In the same period his brother, Louis de la Corne was commandant of the western forts founded mainly by the elder La Vérendrye. Most of his ventures made large profits and, at the time of his death, he was one of the richest men in Canada. Luc de la Corne was an interpreter for Louis-Joseph de Montcalm at the Massacre of Fort William Henry. Saint Luc was held partially responsible for the attack on the British troops and was dismissed.
In 1761, Luc was returning to France, when his ship Auguste ran into terrible weather and sank. The seven endured some terrible hardships but eventually found themselves back in Montreal. The feat made Saint Luc de la Corne famous in Quebec.[2] During the American Revolution War, Saint Luc reappeared as an interpreter for John Burgoyne during his trek to Saratoga. During this campaign two natives of Saint Luc's detachment were found responsible for the killing of Jane McCrea.