Demachy is one of those composers of whom history tells us little. Nevertheless, he is one of the key figures of the French viola da gamba tradition during the reign of Louis XIV. According to Jean Rousseau (Traité de la Viole, 1687), he was a pupil of Nicolas Hotman (1610–1633), like Saint-Colombe (ca.1640–ca.1700).

Demachy left a single collection of 8 suites for solo viol: Pièces de Violle en Musique et en Tablature, differentes les unes des autres, et sur plusieurs Tons.