The contrôleur des armes in the manufactory at Charleville-Mézières.

In May 1777, the American Commissioners contracted with him to repair the arms they purchased from Jean-Joseph-Carié de Montieu. He proved unreliable and trouble ensued.

By the summer of 1778, Jonathan Williams, Jr., the Commissioners’ agent at Nantes, became suspicious of Mercier’s bills, ordered the work stopped, and refused further payments. Mercier engaged a procureur at Nantes and launched an unsuccessful law suit against Williams.