At the start of the Napoleonic Wars in 1805, Marchand led a brigade in the Grande Armée at Haslach-Jungingen and Dürenstein. Promoted to lead a division in Marshal Michel Ney's corps, he fought at Jena and Magdeburg in 1806. Leading an independent force, he defeated 3,000 Prussians late in the year. The following year he led his troops at Eylau, Guttstadt-Deppen, and Friedland. Napoleon bestowed honors and the rank of nobility upon him.