As a boy Oppenord was sent in 1692 to study as a royal pensioner in Rome for eight years, where he largely ignored the remains of Classical Antiquity and spent his time instead sketching the Baroque sculptural ornaments of the preceding generations, principally under Bernini and Borromini, and in northern Italy the ornament of Mannerist architects like Pirro Ligorio. Three notebooks of his youthful drawings survive. On his return to France in 1699 he failed to secure a post in the Bâtiments du Roi. He remained an outsider, never taken into the Académie, but found private commissions, such as the engravings of the collection of the sculptor François Girardon (1710) while he added to his notebooks details of the most advanced recent French decorations, gaining fluency in the French idiom.
Oppenordt, in connection with Robert de Cotte, developed the voluptuous rocaille border and shell ornamentation founded on the Italian Grotesque. The high altar of St. Germain des Prés and that of Saint-Sulpice (1704) gained for him the favour of the regent. He was entrusted with the restoration and decoration of the Château Villers Cotterets, for the reception of the king after his anointing at Reims. In the Palais Royal and the Hotel du Grand Prieur de France he proved himself an elegant decorator. In 1721 the continuation of the work on Saint-Sulpice was transferred to him. He had already built (in 1710) the chapel of St. John the Baptist in the cathedral of Amiens and earlier the Dominican novitiate church in Paris.
He also possessed unusual talent as a draughtsman. Two books of his engraved designs were published, the Grand Oppenord and the Petit Oppenord. In his Dessins, couronnements et amortissements convenables pour dessus de porte etc., Huquier engraved many of Oppenordt's designs.
Oppenord himself wrote (posthumously published) L'Art décoratif du 18 siècle (Paris, 1888). He died in Paris in 1742.