In 1752, he joined the French army. He achieved the rank of colonel and led the infantry regiment "von Fersen". In 1758, he traded it for the cavalry regiment "Nassau-Saarbrücken". During the Seven Years' War, he spent the years 1757 to 1761 fighting in Germany. He fought in the battles of Hastenbeck, Sonderhausen, Lutternberg, Bergen and Minden. He also participated in the sieges of Kassel and Wolfenbüttel and he fought at Grüneberg and Armöneburg. During the Battle of Sonderhausen, he was hit in the left shoulder.