His father Alexandre-Jean Oppenord (1639–1713) was an ébéniste, born Cander-Johan Oppen Oordt[4] at Guelders, one of numerous cabinet-makers from the Low Countries who were drawn to Paris by the opportunity of patronage; the elder Oppenord was naturalized in 1679, when he was a menuisier en ebène ("furniture-maker in ebony") at the Manufacture Royale des Gobelins;[5] in 1684 the elder Oppenord was appointed an ébéniste du Roi, with official lodgings in the Galeries du Louvre that had been perquisites in the royal gift of outstanding craftsmen in the luxury trades since the time of king Henri IV.
As a boy Gilles-Marie Oppenord was trained in the studio of Jules Hardouin-Mansart and 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 those carried out under Bernini and Borromini, and in northern Italy the ornament of Mannerist architects like Pirro Ligorio.
His only known early commissions, for the high altar (demolished) for Saint Germain des Prés, Paris[7] and that of Saint-Sulpice (1704), gained for him the favour of the duc d'Orléans, soon to become Regent: in the year his father died (1713) he was listed as premier architecte of the duke.
In the Palais Royal and the Hôtel du Grand Prieur de France he proved himself an elegant decorator.
In his Dessins, couronnements et amortissements convenables pour dessus de porte etc., Gabriel Huquier engraved many of Oppenordt's designs.