In the War of the Third Coalition, Marchand commanded a brigade in Pierre Dupont de l'Etang's division of Marshal Michel Ney's VI Corps. In the Ulm Campaign, he fought at the remarkable Battle of Haslach-Jungingen, where Dupont's 5,350 infantry, 2,169 cavalry, and 18 guns held off 25,000 Austrians. The French lost 1,500 killed and wounded plus 11 guns and 900 men captured. Austrian losses numbered 1,100 killed and wounded, with 3,000 more captured. During the pursuit of Franz von Werneck's corps, Dupont's division fought in clashes at Herbrechtingen and Neresheim on 17–18 October. Marchand fought at the Battle of Dürenstein on 11 November.