 The couple were wed in 1781 and their eldest son became the fifth Baron de Longueuil in 1841.Grant took part in the defence of the town of Quebec during the American invasion of 1775-6 and some of his property was damaged during this period.He was a member of the historical Legislative Council of the Province of Quebec from 1777 to 1791 and served as deputy receiver general from 1777 to 1784.