In September of the same year, he joined a French military force under Napper Tandy with the rank of Captain and sailed from Dunkirk with arms and ammunition for Ireland.
The expedition had to turn back following the defeat of General Humbert and arriving in Hamburg they were handed over to the British authorities and taken to Ireland, where they were imprisoned in Kilmainham Jail.
Following the death of his brother Thomas (who was also in the Legion) in a duel with another officer, he was transferred to the 70th Regiment of the line, where he served in Massena's expedition to Portugal, and distinguished himself in the retreat from Torres Vedras and the battle of Sabugal.
In the period of the Bourbon Restoration, his friendship with the opposition leader, General Foy, placed him under some suspicion, but in 1828 he was selected by Marshal Maison to accompany him on an expedition against Ibrahim Pasha in Morea, Greece.
After serving as governor of Navarino, Messinia, and Nafplio, he relieved Argos from the attack of Kolocotronis, who was then acting in the interest of Russia and Count Capo d'Istria, and defeated him.