Engineer, freemason and politician. Sagasta became engineer of roads, canals and bridges at a very young age and in 1857 he was already professor at the School of Public Works Assistants (l’Escola d’Ajudants d’Obres Públiques). In 1866 he took part in the revolt of the barracks of Sant Gil (caserna de Sant Gil). He went into exile to France until the 1868 Gloriosa Revolution, in which he took an active part. 

Sagasta was appointed Minister of the Interior during the provisional government of Francisco Serrano, and twice President of the Council of Ministers, in 1871 during the reign of Amadeus of Savoy, and in 1874. Before the Bourbon Restoration, he was the leader of the Constitutional Party, and in 1880 he founded the Liberal Party. He was a great defender of the democratic monarchy, and was frontally opposed to Manuel Ruiz Zorrilla, who founded the Democratic-Radical party. After the Bourbon Restoration, he tried to defend the Constitution of 1869 and worked to establish a more democratic and progressive government. In 1885, he managed to unite several Republican leaders in the Liberal Party. His party was in power in alternance with Cánovas del Castillo’s conservative party. Sagasta could not prevent the Cuban insurrection and assumed the loss of the colony in 1898.

Sagasta is also known for being in charge of making anarchism illicit.