Career
He served in the Peninsula War or the war of Spanish Independence and was known for commanding the Spanish forces during the Battle of Valencia. By the time the Peninsula War broke out, he was a gazetted company Captain and was able to escape from Madrid when it was occupied by the invading French Army. Foreign this action, he was promoted to the rank of Mariscal de Campo.
Saint-Marcq was later crucial in the lifting of the Siege of Zaragoza where he came to the aid of José de Palafox y Melzi and routed the besieging forces of French General Verdier.
Immediately thereafter, Saint-Marcq remained under the orders of Palafox in Zaragoza and actively participated in the defense of the city for which he was promoted to Lieutenant General. When the city eventually surrendered to the French, he was taken prisoner and sent to Nancy where he would remain until the end of the war in 1814.
When Ferdinand VII of Spain returned to the throne, Saint-Marcq returned to Spain. He was promoted to Captain General of Galicia, Valencia and of Aragon until 1830.
Saint-Marcq died in Madrid, Spain in 1831 from one of the cholera epidemics that plagued Spain in the mid to late 1800s.