His parents were Francisco José Díaz Vélez, a wealthy merchant born in Huelva, Spain who was former chapter of Buenos Aires Cabildo, and María Petrona Sánchez Araoz de Lamadrid, a native of Tucumán, Argentina from an important colonial family.

The following year, during the second British Invasion, distinguished himself in the Defense of Buenos Aires with the Patricians under the command of Cornelio Saavedra, and submitted the English in the "House of the Widow Virreyna (Viceroy)", between 2 and 7 July.

He actively supported the May Revolution, participating in the meetings that decided the dismissal of Viceroy Baltasar Hidalgo de Cisneros, attending the one of May 19, called by Nicolás Rodríguez Peña.

But as these guards were composed of the body of the patricians who was most touched by the insurrectionary spirit, and as they were under the command of Captain Don Eustaquio Díaz Vélez, who was one of the boldest officers and most developed in the riot, the result was that so far from the entrance clogged it lavishly provided to all who submitted their note with the sign or signal agreed between the patriots, while at the other side was allowed to enter only the personages well known for his official position, opposing difficulties and insurmountable observations to all those who could be taken as strangers or persons of lower position, especially if they were Europeans.

That night, he met at Rodriguez Peña home, with Domingo French, Feliciano Antonio Chiclana and other conspirators who managed the resignation of its members and demanded that the cabildo "proceeds with other election in persons that may merit the confidence of the people, course that do not deserve the ones that constitute the present Board, believing that will be the means of calming the agitation and excitement that was renovated between people.... " Emerged the Primera Junta of Government, it entrusted his first military mission to occupy the square of Colonia del Sacramento, in the Banda Oriental, whose population sympathized with the revolutionary patriots, beating its garrison and carrying large amount of ammunition to Buenos Aires.

He was part of the Army of the North (Spanish: Ejército del Norte) that the Board of Buenos Aires had sent to military aid the Intendencias of the Upper Peru and participated in the defeated of Cotagaita.

Weeks later, on November 7, 1810, he fought in the Battle of Suipacha, first win rioplatenses revolutionary arms, which allowed the rise of the cities of Potosí, Chuquisaca and La Paz, opening the patriots all the Upper Peru.

Díaz Vélez, in a letter sent to the revolutionary authorities in Buenos Aires regarding the causes and responsibilities Huaqui's defeat, dated August 29, 1811, held that anything they did not get the Jujuy forces forward ever would Perú.

Pueyrredón, after taking the treasure of Potosi Mint, fearing a loss and wanting to play a political role in the First Triumvirate formed in Buenos Aires, called for his release, although previously he sent the reinforcements he was able to, to Díaz Vélez when he knew of the movements of Colonel Picoaga royalist forces.

Díaz Vélez routed royalist Colonel Barreda at the action of Cangrejillos and, on January 12, 1812 he fought, in the gorge located along the river Suipacha, the Battle of Nazareno, against Picoaga.

Díaz Vélez, noting that it was alone and without cavalry troops, cautious and steady as usual, managed to take the park of Brigadier Pío Tristán, with thirty-nine wagons loaded with arms, ammunition, some of the guns and hundreds of prisoners.

Encased in it, protected by moats, Díaz Vélez waited expectantly as the winner because in large part, by his actions, he decided the victory of the revolution weapons that day.

His last attempt was using diplomatic channels: under the intimation of surrender within two hours made by the realistic chief threatened to burn down the city, Díaz Vélez vehemently replied, inviting him to dare, as the patriotic troops were victorious and inside were 354 prisoners, 120 women, 18 ox carts, all rifle ammunition and cannon, 8 guns, 32 officers and 3 chaplains taken to the royal army.

... Major General, D. Eustoquio Díaz Vélez, who commanded it, was one of those men whose existence had always been attached to the homeland ... with its strong response, undid his faint hope and made him a confused and shameful retreat.

A few days later, at the Battle of Salta, on February 20, 1813, Díaz Vélez directed an Argentina cavalry wing and although was badly wounded, the coontation was a new and major victory for the patriot weapons.

After the Battle of Salta, in which first flamed the homeland sign in an act of war, the flag was placed on the balcony of the Cabildo by Eustoquio Díaz Vélez and the trophies took away to the realists located in the Chapter House.

The dispatch ordered the following: Inasmuch as attending the distinguished services, adherence to a system of freedom, military talents, proven value and known ability of Colonel of the Regiment of Mounted Grenadiers D. José de San Martín, came to confer employment of Major-General of the Heplper Army of Perú, that served in commission of the same cavalry class Line D. Eustoquio Díaz Vélez, giving him thanks, exemptions and privileges that for this title correspond.

But, looking to avoid a civil war, and in order that the people of Santa Fe, Entre Ríos, Corrientes and the Banda Oriental send deputies to the Congress of Tucumán he signed -the day 9- with the commander of the naval forces of Santa Fe the Santo Tomé pact, by which the Army of Observation deposed interim director Ignacio Álvarez Thomas, transferred its headquarters to Díaz Vélez, replacing Belgrano and agreed that a final peace should be ratified by both governments and also be accepted by Artigas.

A few days after the pact was unknown, Governor Vera attacked the city of Santa Fe and managed to reconquer it, Díaz Vélez was forced to leave because of unsuccessful efforts of the Commissioners (Commission of Real Strange) -lawyers doctors Alejo Castex and Miguel Mariano de Villegas, next to the counter Antonio Pósiga- to the government of the Province of Santa Fe to agree on terms for a ceasefire, "authorized to bargain with the chief of that territory the transaction of the unfortunately existing differences between the two territories".

Díaz Vélez returned to Buenos Aires, where he was part of the renewed Lautaro Lodge, created at the initiative of José de San Martín, who tried to remedy his discredit, trying vainly to make resurgence after the fall of the Director Alvear.

The most important police reforms were: the creation of a single command for operation, the implementation of the "security ticket" or identity record of the persons, the transfer of the administration of the lottery game which was in private hands and the lamentation of the abolition of flogging to which they were subjected children in schools.

Produced the Arequito Revolt and in front of the war against the littoral, the chief of the Military Staff, Saavedra, on 28 January 1820 urged the sovereign Congress to adopt strong measures to remedy the precarious state of the army.

Thanks to it Díaz Vélez returned to Buenos Aires and in October of that year, was tabled to active duty being comprised in the provisions of the Military Reform Law, so he retired on February 26, 1822 with full pay.

Juan Manuel de Rosas in the province organized a general protest against this policy and revolted in Chascomús, put in prison, he was released quickly due to popular pressure.

The governor of the province of Buenos Aires Manuel Dorrego, through a decree dated on January 2, 1828 named Díaz Vélez, for that year, Chascomús Justice of the Peace.

He started the peaceful business with the friendly border Indians that in the interior of the same but because of the large expanses of fields and little existing population in an area exposed to dangers this system did not give the expected results.

When they reach the estancias by necessity and but by force must give the fillies and mares to remain and to take to their tents, under the penalty of not doing so are threatened the owners and hated and exposed to arreen them the herds of the field.

To help the defence of the city, General Díaz Vélez formed on 16 February of that same year the Argentina Legion, composed of more than five hundred Argentine volunteers, whose officers were exiled for political reasons both unitary and federal.

By then, it was usual that, due to the large distances to cover and the lack of suitable communication, the national guard arrived late to the scene, when the Mapuche had looted the town and the countryside, taking everything that was useful to them.

Brave as it had been throughout his life, Díaz Vélez, not only did not leave his estancia, but he supplied in it giving refuge and shelter to the gauchos and peasants of the region and prepared, with the few weapons that he possessed, to defend.