Téllez-Girón held important commands during the War of the Pyrenees which began on 7 March 1793 and ended with the Peace of Basel on 22 July 1795. As a Lieutenant General, he commanded a column under Captain General Antonio Ricardos in the Battle of Mas Deu in the eastern Pyrenees on 19 May 1793. Soon after the battle, he transferred out of Ricardos' Army of Catalonia. He later fought in the western Pyrenees. In the fall of 1794, he was placed in charge of the defense of Navarre. The Army of the western Pyrenees under French General Bon-Adrien Jeannot de Moncey defeated his badly outnumbered troops in the Battle of Orbaitzeta in October 1794, though he was able to keep the French from capturing the city of Pamplona.