He began his military career in the artillery of Buenos Aires, during the Spanish–Portuguese War, staying in that unit until the signing of the First Treaty of San Ildefonso that incorporated the Banda Oriental to the Viceroyalty of the Río de la Plata. With the war concluded, he became a "regidor" of the Buenos Aires Cabildo. He took the arms again in 1778, during an attack of the natives, and directed the operations at the fort in San Miguel del Monte. As Spain was fighting in the American Revolutionary War against Great Britain, it was suspected that the British might launch an offensive against the Spanish colonies. Azcuénaga led an artillery unit with 4 cannons in 1781, but no British attack took place.