In 1806, Debilly was still a brigade commander, but in the I. Division of the III. Corps of Marshal Louis-Nicolas Davout. The 10,000-man I. Division on the French left flank at Auerstadt. Jean Louis Debilly commanded the leading brigade of French infantry marching on Hassenhausen in late morning of 14 October. Facing a cavalry charge, Debilly ordered the infantry to form defensive squares. The infantry absorbed the brunt of a triple Prussian cavalry charge; when the Prussian cavalry recoiled under heavy musketry-fire, the brigade reformed its line and marched against the supporting Prussian infantry, pushing them back to Lissbach. In the course of this advance, Debilly was killed.