Van Omphal began his active service during the Kingdom of Holland. Part of the Dutch expeditionary force to Spain, he participated in the Battle of Ciudad Real. In 1810, the kingdom was annexed by the First French Empire and the Dutch forces were incorporated in the French army. As a result, in 1812 Van Omphal took part in the French invasion of Russia; he was one of the few Dutch survivors. He was noted for his courage during the Battle of Leipzig (16–18 October 1813); at the time he was a first lieutenant for the second regiment of lancers of the Imperial Guard of Napoleon I.