Promoted to the top military rank of General of Division in 1803, Nansouty was called to the command of the 1st Heavy Cavalry Division in Emperor Napoleon I's newly created Grande Armée. Commanding this division from 1804 to 1809, Nansouty was present at some of the most significant battles of the Third, Fourth and Fifth coalitions, leading cavalry actions at the battles of Austerlitz, Friedland, Eckmühl, Aspern-Essling and Wagram. In 1812, during the campaign in Russia, Nansouty commanded the I Cavalry Corps, which he led with distinction at such battles as Ostrovno and Borodino, where he received a severe knee wound. The next year, he commanded the Imperial Guard cavalry, which he led at Dresden, Leipzig and Hanau, where he was again wounded. In 1814 he led his men in several engagements, including La Rothière, Montmirail, Vauchamps and Craonne until his incapacitation from wounds that year.