Charles was known as the Count of Harcourt-Elbeuf while his father was alive; from circa 1650, he styled himself as the "prince d'Harcourt", the county of Harcourt being one of the subsidiary titles of his father. He served in Italy (1641) and Picardy (1642) under the command of his uncle Henri, Count of Harcourt. Charles took great part in the Thirty Years' War; he was with "le Grand Condé" (then the Duke of Enghien) at the famous victory at Rocroi in 1643. Charles was also a part of battles at Thionville and Sierck, as well as the siege of Gravelines (1644); he latter fought in the Battle of Nördlingen (1645) as well as at Trier.