After the close of the Seven Years' War he was sent to search in the archives of Great Britain for documents bearing upon the history of France, more particularly upon that of the French provinces which once belonged to England.
A useful selection of these documents was published (unfortunately without adequate critical treatment) by Jacques Joseph Champollion-Figeac, under the title Letters of Kings, Queens and Other Persons of the Courts of France and England, from Louis VII to Henry IV (Lettres de rois, reines et autres personages des cours de France et d'Angleterre, depuis Louis VII.
These were included in the collection of the Académie des Inscriptions: This last was read to the Academy on 22 January 1793, the morrow of Louis XVI's execution.
To the Chronological Table of Diplomas, Charters, Letters, and Printed Acts Concerning the History of France (Table chronologique des diplômes, chartes, lettres, et actes imprimés concernant l'histoire de France) he contributed three volumes in collaboration with Mouchet (1769–1783).
Charged with the supervision of a large collection of documents bearing on French history, analogous to Rymer's Foedera, he published the first volume (Diplomas, Charters, Letters, and Other Documents Relating to French Affairs, etc., in Latin: Diplomata, chartae, epistolae, et alia documenta, ad res Francicas spectantia, etc., 1791).
IV of the Chronological Table of Diplomas (1836); Champollion-Figeac's preface to the Letters of Kings and Queens; the Committee of Historical Works (Comité des travaux historiques), by X. Charmes, vol.