Napoleon's Irish Legion (French: Légion irlandaise) was a French light infantry battalion established in 1803 for an anticipated invasion of Ireland. It was later expanded to a four battalion regiment with a depot and won distinction in the Walcheren Expedition and the Peninsular War. It was disbanded in 1815.
The first officers included Irish rebels taken during the 1798 rebellion who were freed during the short peace effected by the Treaty of Amiens on condition of exile, and who had sailed for France in June 1802. The treaty broke down in May 1803 with the start of the War of the Third Coalition. As a part of Napoleon's planned invasion of the United Kingdom in 1803-05, the Irish Legion was to provide the indigenous core for a much larger invasion force of 20,000 earmarked to take Ireland, known as the Corps d'Irlande.
The Legion was established on August 31, 1803 in Morlaix, France. Bernard MacSheehy was assigned to form the regiment he was an Adjutant-General in Napoleon's army.
The purpose of the Legion was to align the Irish hearts to the French cause in the imminent invasion of Ireland. General Pierre Augereau had been ordained to lead the invasion, and wanted Irishmen to serve in his army. However, the Battle of Cape Finisterre and the Battle of Trafalgar in 1805 made a safe sea crossing uncertain at best, and Napoleon was forced to abandon his plans for Ireland. He shifted his focus towards Austria and Eastern Europe and launched the Austerlitz campaign in late 1805. The legion remained on the French coast on garrison duty and coastal defence.
The Legion was eventually expanded from a battalion to a regiment and there was greater demand for more soldiers. These made a varied group; some came from Ireland, some had been pressed into the Royal Navy and escaped, and some were German or Polish. While the Legion was stationed at Mainz in 1806, they were joined by 1,500 Poles together with around 200 former United Irishmen who had been sold by the British Government following the recent Irish risings to Prussia to labour in her salt mines and had later joined the Prussian army. Its headquarters was at 's-Hertogenbosch, known to the French as Bois-le-Duc, in what was then the Kingdom of Holland.