See Chef-D'Oeuvre De Le Franc De Pompignan, Jean Galbert de Campistron, Paris 1788 (in French: digital facsimile available at [1]) for some biographical details as well as a contemporary (four years after his death), somewhat hagiographic commentary on three of his best-considered theatrical works. The frontispiece of this work is an engraving of a younger Lefranc, incidentally giving the date of his death as 4 - not 1 as above - November 1784.
societes-savantes-toulouse.asso.fr
"In 1757, a good marriage to the ambitious Parisian Marie-Antoinette Felicité de Caulaincourt, widow of Pierre Grimod du Fort, chief paymaster of the Postes et Relais de France, encouraged him to search for literary glory." - CrangaArchived 2011-05-31 at the Wayback Machine (in French), p 187.
web.archive.org
"In 1757, a good marriage to the ambitious Parisian Marie-Antoinette Felicité de Caulaincourt, widow of Pierre Grimod du Fort, chief paymaster of the Postes et Relais de France, encouraged him to search for literary glory." - CrangaArchived 2011-05-31 at the Wayback Machine (in French), p 187.