From the youngest age he participated in the wars which France led almost continuously at the time. In 1557, he, together with his father, was taken prisoner after the Battle of St. Quentin. In 1562 in the course of the French Wars of Religion he participated in the Battle of Dreux, where his father headed the Catholic army against the Huguenots. In 1563, king Charles IX made him the lieutenant general of Paris and Ile-de-France. Further, Charles de Montmorency participated in the Battle of Saint-Denis in 1567 and subsequently was named the colonel general of the Swiss. In 1569, he participated in the Battle of Moncontour, and in 1572—1573, in the siege of La Rochelle. In 1574, however, Charles de Montmorency got out of favor and had to retire to the countryside.