 Of aristocratic descent, his father was Claude-Florimond de Faÿ, comte de Coisse (1712–1790) and his mother was Marie-Françoise (1712–1793), daughter of Nicolas de Vachon, .De Faÿ joined the French Army as a "Sous-lieutenant" in the Gardes du Corps.He was promoted Colonel of the 3rd Chasseurs-à-Cheval Regiment, 5 February 1792, before serving at Philippeville, Grisvelle and Maubeuge.