From 1805 onwards, Saint-Hilaire would continually serve in the "Grande Armée", holding various divisional commands. In 1805, he commanded a division in Marshal Jean-de-Dieu Soult's IV Corps during the War of the Third Coalition and at the Battle of Austerlitz, he led a decisive assault on the Pratzen plateau, receiving a serious wound at the beginning of the assault but nonetheless retaining his command for the rest of the battle. Between 1806 and 1807, he fought with distinction at Jena, Eylau and Heilsberg. He was made a Count of the Empire in 1808 and received a divisional command in the Army of Germany, with which he would campaign in southern Germany and Austria. On 22 April 1809, Saint-Hilaire distinguished himself under Napoleon's eyes at the Battle of Eckmühl.