French Noble Name Generator

No. Plenty of commoners carried de as part of a place-based surname, and some noble families had no particle at all. In noble names the particle points to the family's seat, and the real signals of rank are the house itself, a title (comte, marquis, duc) and the hyphenated branch names that show descent from a known line.

Duc (duke) was the highest rank below prince, followed by marquis, comte (count), vicomte and baron. The feminine forms are duchesse, marquise, comtesse, vicomtesse and baronne. Under the old regime the title was tied to a piece of land, which is why a single man could be known by his family name and by a separate title estate.

Many are: Montmorency, Rohan, La Rochefoucauld, Noailles, Gramont, Harcourt, Lévis, Crussol and Talleyrand-Périgord were among the great houses, and several names on the list belong to well-known historical figures. The list also includes invented seats such as Vauclair, Roncevaux and Chantemerle for characters you do not want tied to a real lineage.

Pick a given name from the right century, attach de or d' and a seat, and add a hyphenated second seat if the character belongs to a cadet branch. Give the title separately in prose (le marquis de Varennes) and, for an original world, swap in an invented estate ending in -mont, -court, -ville or -ay so the name sounds French without pointing at a real family.