Desnos, born in a small village close to Beauvais, was apprenticed to Joseph-Simon Guibot, 'maître fondeur' at the quai de l'Horloge in Paris. In 1749 he took over the globe workshop of the Hardys, after marrying the widow of Nicholas Hardy (who had died in 1744), Marie-Charlotte Loye. Desnos first continued to work at the Hardy place in the rue Saint-Julien-le-Pauvre in Paris, but in 1757, when he became a freeman, he moved to a new place, at the sign of the Globe in rue Saint-Jacques. From 1759 he called himself 'ingénieur-géographe et libraire du roi de Danemark'. In the 1760's Desnos extended his activities as a publisher of maps and books. Globe making became less important for him, perhaps because of the success of his main competitor Didier Robert de Vaugondy. For meeting such competition Desnos turned to more special objects such as the Sphère mouvante, advertised in his sales catalogue of 1775.
Desnos is also known to have collaborated with the map publisher and Géographe du Roy Jean-Baptiste Nolin the younger (1686-1762) and to have produced globes of 6¼-, 8½-, 10¼- and 12¾-inches diameter. His first globe, a 6¼-inch diameter celestial globe, is dated 1742. In 1758 Desnos participated in an important step forward in the presentation of celestial maps and globes when he was one of the first publishers to utilise the information gathered by the French astronomer l'Abbé De La Caille (1713-1762), as on this example. La Caille catalogued 9,800 southern stars from the Cape of Good Hope, and invented fourteen new constellations. It was La Caille who with the chart drawn up from the discoveries of this expedition, initiated the convention of the depiction of constellations by scientific instruments alongside the traditional mythical figures and beasts, a convention Desnos was one of the first to adopt.