In the run up to the Battle of Quebec his cousin, Vaudreuil, employed him to build defences about the city, and during the battle he served as his aide-de-camp. In 1760 he was put in charge of fortifying Ile aux Noix to impede the British advance from the south, but was forced to fall back to Montreal, Quebec. Another of his first cousins, Nicolas Renaud d'Avene des Meloizes-Fresnoy (1729-1803), Marquis de Fresnoy, served as major-general in the French victory at the Battle of Sainte-Foy, for which he was rewarded the Grand Cross Order of Saint Louis. After the capitulation, Lotbiniere left his wife and newly born daughter in Canada and returned to France with his 12-year-old son, cadet Michel-Eustache-Gaspard-Alain Chartier de Lotbinière.