Sebastián first studied at the San Julián school, close to his house, on the banks of the Barbadún river; Later, since his father wanted to direct his career towards the Court, he went to Madrid in 1700, to serve as a page for José de Grimaldo (who would later be Secretary of War and Finance).

Jaime Vélaz de Medrano y Barros, III Marquess of Tabuérniga made contact with Sebastian in August 1746 - setting out proposed British terms for a peace agreement.

For his service he was made Marqués de Villarías by King Philip V of Spain on 22 March 1739, an honour awarded sometimes either to outgoing First Ministers or during their tenure.

From these assemblies, in 1744, Olivieri and the Marquis of Villarías drafted a project for the foundation of the Royal Academy of Fine Arts entitled "Rules that are proposed to the Hon.

Mr. Marqués de Villarías so that after two years of practice that seem convenient for now, they can contribute to the formation of laws for the Academy of Sculpture, Painting and Architecture that is intended to be founded in Madrid under the protection of the King".

In this way, he was required to occupy positions of the lordship (alderman in 1730 and deputy general in 1740) and from 1722 he enjoyed the provost of the towns of Ondárroa, Guernica and Bermeo, which were administered by his older brother Agustín.

On the other hand, he carried out patronage work in his small homeland, diverting a large flow of capital to collaborate in economic needs and to make different donations in the community.

Taking advantage of the new plant, he was able to build a chapel next to the gospel dedicated to Saint Clement, where his coat of arms is displayed, as well as the Carrara marble bust of his figure.

Already ill and without having married, the Marquis of Villarías made his will on March 9, 1766, naming his brother Agustín as universal and sole heir, and in the event of his death, his nephew Simón de la Cuadra.

All the houses, lands and other possessions that in that town of Villarías and Merindad de Castilla la Vieja, his brother Agustín had bought as a result of the orders that he had given him for this, were also joined.

Sebastian died in Madrid on April 23, 1766, at the age of seventy-nine, and was buried the following day in the church of the convent of the Agonizing Sick Ministers Regular Clergy Fathers, on Fuencarral de la Villa y Corte street.