For a short time he served with Gaspar de Jáuregui, another Gipuzkoan known as "The Shepherd" (Basque: Artzaia), one of the guerrilla leaders, who later became a general in the regular army against which Zumalacarregui fought.

But Zumalacárregui, who was noted for his grave and silent disposition and his strong religious principles, disliked the disorderly life of the guerrillas, and when regular forces were organized in the north he entered the 1st battalion of Gipuzkoa as an officer.

His brother Miguel Antonio de Zumalacárregui was in Cádiz at the time the Cortes passed the Constitution of 1812, going on to be elected chief deputy of Gipuzkoa.

[1] The proclamation of the king's daughter Isabel as heiress was almost the occasion of an armed conflict between him and the naval authorities at Ferrol, who were partisans of the liberal and so-called "constitutional" cause.

When the Carlist uprising began on the death of Ferdinand VII, he is said to have held back because he knew that the first leaders would be politicians and talkers.

Yet by the beginning of June 1835 he had made the Carlist cause triumphant to the north of the Ebro, and had formed an army of more than 30,000 men, of much better quality than the constitutional forces.

If Zumalacárregui had been allowed to follow his own plans, which were to concentrate his forces and march on Madrid, firstly seizing Logroño (La Rioja, Castile), he might well have put Don Carlos in possession of the capital.

[1] The wound was trifling and would probably have been cured with ease, but Zumalacárregui decided to employ a famous Gipuzkoan quack called "Petriquillo", whom he trusted.

Zumalacárregui is often popularly credited as the inventor of Spanish omelette (or tortilla de patatas), which he allegedly elaborated during the Siege of Bilbao, as a simple, fast and nutritious dish with which to satisfy the hardships of the Carlist Army.

The increasing ferocity of the war, substantiated in routine executions of Carlist soldiers and officers, convinced him of the necessity of a similar retaliation against the liberal forces.

Zumalacárregui, however, would later sign the Lord Eliot Convention, shortly before his own death, which aimed to end the indiscriminate executions by firing squad of prisoners on both sides.

Of Zumalacárregui, Henningsen writes: Now that Zumalacarregui's memory must descend, whatever be the issue of the contest, as an heir-loom to all classes of his countrymen, as long as the Spanish language endures, and that his name must be mingled in the songs of the peasantry with that of the Cid, it would be superfluous to say that he was no ordinary man; but, although, on the roll of those who have acquired a title to immortality, by the immense share he had in the early successes of the Royalist army, justice is scarcely done him.

It is doubtless that it required the iron frame and indomitable spirit of the mountaineers he commanded, to battle so long against man, want, and the elements.In 2017 the People's Party of the Basque Country called for a street named after him to be renamed.