This choice was probably to keep political favor with the new rulers of Canada as his father had been in constant and open opposition to British rule for which in 1784 he had been awarded the Marquisate.

In France, he resumed his studies with the thought of joining the French cavalry, but following the Treaty of Paris (1763) and the consequent loss of his father's land in America, he returned to Quebec and was commissioned as a military surveyor in 1768.

After the American invasion of Montreal in 1775, he was one of the first Canadian seigneurs to offer his services to the Governor Guy Carleton, 1st Baron Dorchester.

He helped to defend Fort St Johns (later Saint-Jean-sur-Richelieu) against the Americans, but was captured and taken prisoner by them and removed to Albany, New York.

The moment is captured in a painting by Charles Huot which hangs above the Speaker's Chair in the present-day National Assembly of Quebec.

In this speech, recorded in the Quebec Gazette on 31 January 1793, he asked for French and English to be given equal recognition in the House, Since the majority of our constituents are placed in a special situation, we are obliged to depart from the ordinary rules and forced to ask for the use of a language which is not that of the empire; but, being as fair to others as we hope they will be to us, we should not want our language eventually to banish that of His Majesty’s other subjects.

Joly de Lotbinière also served as Prime Minister of Quebec and Lieutenant Governor of British Columbia.