His father was Jean-Baptiste de Lafontaine, a musician of King Louis XIV at Versailles, and his mother was Bernardine Jouin.
[1] Lafontaine entered a partnership for ten years with his father-in-law, François-Joseph Bissot (1673–1737), to trade with the Indians and hunt seals at Mingan on the Labrador coast.
[5] In 1737 Lafontaine was involved in a quarrel between the governor and the intendant when it was found that Hocquart had given François-Étienne Cugnet a lease on Tadoussac for a very low annual payment of 4,500 livres.
[6] From November 1740 to September 1741 Lafontaine was interim lieutenant general at Montreal for civil and criminal affairs in the royal jurisdiction.
His business affairs expanded to include land on the côte Saint-Jean, a whale-fishing concession at a place named Apetépy on the Labrador coast and a sawmill on the Chaudière River, funded through loans and partnerships.
[1] A detailed inventory of his property by the notary Lemaitre La Morille on 11 July 1765 listed just five books: Pratique civile et criminelle (Civil and Criminal Practice) by M. Lange, Philosophie morale (Moral Philosophy) by Louis Delanclache, Dictionnaire français-latin (French–Latin Dictionary), Oeuvres de Virgile (Works of Virgil) and Instructions generales sur la juridiction consulaire (General instructions on consular jurisdiction).