As a youngster, François joined the regiment his father was serving in, and in 1754 was promoted to the rank of Lieutenant. In 1755 he travelled to Constantinople, the]] of the Ottoman Empire, as the secretary of his uncle Charles Gravier, comte de Vergennes, who had been appointed ambassador. His main duty was to learn the Turkish language, to investigate the situation in the Ottoman Empire and to gather information about the Crimean Khanate.