Reinstated as a chef d'escadron, Jennings served in the French Revolutionary Wars. He was a Corps Commander under Charles François Dumouriez and Lafayette. He performed with great valor at the Battle of Valmy in September 1792, when a unit of hussars under his command saved a whole French division from annihilation. In November 1792 at the Battle of Jemappes, he fought with remarkable bravery. When that battle seemed lost, Kilmaine and the Duke of Chartres (Louis Philippe) turned apparent defeat into victory. On the field he was raised to the rank of Chief Colonel, and from that day was ever afterwards known as "le brillant et courageux Kilmaine".