Trained in the hospital services of Pelletan and Vicq d’Azyr, he also studied under John Hunter in London and Desbois de Rochefort and Boyer in France.

In trying to perfect his skills he made several journeys to England and Italy (spending 4 years at Florence and Siena then Rome and Naples), where his good manners brought him the acquaintance of many of the most distinguished scholars of the day.

Returning to France in the course of 1789, he was made a doctor at Montpellier, in the wake of his remarkable thesis entitled : Essai physiologique sur les vaisseaux lymphatiques (Physiological essay on the lymphatic vessels).

The events of 1792 and early 1793 had caused the whole of Europe to take up arms against France and so, on the advice of his former teacher Vicq-d’Azyr and driven by a desire to serve the Republican fatherland, he got himself sent as a surgeon to the army gathering on the borders of Italy in February 1793.

He soon became one of the top army surgeons through his energy and courage, and in March 1793 was attached to the field hospital of the armée de la Méditerranée due to his knowing Italian.

After this expedition, he rejoined the active army at Albenga, where he learned that on Barras's request and Bonaparte's recommendation he had on 7 brumaire year IV been made "médecin ordinaire" of the hospital of Val-de-Grâce and of the 17e division militaire (Paris).

In this, after tracing their history and giving details of the magnificent collection of them at Florence, he called on the French government to found a similar institution in Paris.

On returning to Paris after the Treaty of Campo Formio, Bonaparte obtained his protégé Desgenettes an attachment to the armée d'Angleterre on 23 nivôse year VI; it is now known that the organisation of this army on the Channel coast was only a cover for preparations for the French invasion of Egypt.

In 1798, he was made chief physician of the Armée d'Orient as well as part of the natural history and physics section of the Institut d'Égypte, and Bonaparte invited him on board the admiral's flagship Orient.

[2] Desgenettes had hardly arrived in Egypt when he was assailed by the several diseases brought on the army by the burning heat, continual bivouacing and lack of drinkable water.

The many cases of smallpox, scurvy, "fièvre de Damiette", severe and contagious conjunctivitis and dysentery observed by him here gave him further experience of military medicine.

On 6 April 1807, Desgenettes received the emperor's order to rejoin the grand quartier général; his only son was dying, but he stopped caring for him and left with 24 hours.

Loaded with favours from Napoleon but despairing at the curbs set by his army work on his liberty and independence, he was made a knight of the empire in 1809, then a baron in 1810.

Tsar Alexander I of Russia freed him when he heard of the care he had taken of Russian soldiers and had him escorted by his Cossack guard to the French forward-lines at Magdeburg on 20 March 1813.