Godefroy de Tonnancour received his commission as a lieutenant in the militia in 1803 and served as a captain during the War of 1812, later reaching the rank of lieutenant-colonel.
He became co-seigneur of Yamaska in 1834 following the death of his father.
Elected to the assembly in April 1820, Godefroy de Tonnancour did not run for reelection in the election held in July 1820.