Charged to prepare for an expedition to Ireland, he took command of the Légion Noire under Hoche, sailing in the ill-fated Expédition d'Irlande to Bantry Bay in 1796, and was engaged in actions at sea against the Royal Navy.
On his return to France, Humbert served in the Army of Sambre and Meuse, before being appointed to command French troops in an attempt to support the Irish Rebellion of 1798.
The expedition was able to land in Ireland at Killala on Thursday 23 August 1798, meeting with initial success in the Battle of Castlebar where they routed the Irish Militia.
[3][4] Humbert was shortly repatriated in a prisoner exchange and appointed in succession to the armies of Mainz, the Danube and Helvetia, with which he served at the Second Battle of Zurich.
Humbert was accused of looting in Saint-Domingue by Jean Baptiste Brunet, and was also rumored to be having an affair with Pauline Bonaparte, the wife of his commanding officer Charles Leclerc.
General Andrew Jackson thanked him for his assistance there after the American victory in January 1815, and thereafter Humbert lived peacefully as a schoolteacher until his death.