During the War of the Pyrenees (1793–1795) against France he took part in many notable actions, was wounded, and spent 75 days under fire at the siege of Collioure.

The Cortes of Cádiz – which served as a parliamentary Regency after Ferdinand VII was deposed – named Álvarez commander of the Army of Catalonia and Governor of Girona.

On 21 January 1809 Álvarez was brought to the castle of San Fernando in Figueres, where he was found dead the following day, of a fever according to the French, poisoned, according to the Spanish.

[4][1] He was posthumously promoted to Field Marshal in April 1809 and made a Commander of the First Battalion of the Spanish Royal Guards Regiment in May 1810.

In 1815 a black marble tablet was placed on his grave which stated that Álvarez had been poisoned, and was a Victim of the Iniquity of the French Tyrant.