During the War of the Second Coalition, he served as Chief of Staff to Jean Victor Marie Moreau in the Italian theatre, where he distinguished himself at Noir in 1799.

He defeated the Austrians in the Valtellina in 1800, where under his command, French forces killed 1,200, captured 4,000 men, and eighteen pieces of cannon.

In the Year XII, he entered into extraordinary service, and remained a member of the Council of Administration of War (Conseil d'Administration de la Guerre) until 1805.

Napoléon wrote to Fouché on the subject:Je vous dirais que le général Desolles a tenu en confidence des propos fort extraordinaires qui montreraient l'existence d'une petite clique aussi envenimée que lâche.

Eventually winning back imperial favour, he did not return to the State Council (Conseil d'État), and from 1808 to 1810 he commanded a division in Spain, during the Peninsular War.

[1] Left behind was only one brigade of Dessolles's division, with a few Spanish levies, with which Augustin Daniel Belliard, the governor of the city, was expected to hold the capital; some 4,000 men, in all.

These favours were rewards for his efforts convincing Emperor Alexander I of Russia to reject the proposed Habsburg-Bonaparte regency of Empress Marie-Louise, and instead supporting the restoration of the French Bourbons.