He oversaw such cases as those of the ETA militant Josu Urrutikoetxea, and of Manuel Charlín, head of the Los Charlines drug trafficking family.

He and fellow magistrate Baltasar Garzón were persuaded into politics by PSOE prime minister Felipe González in order to give the party a moral image after scandals.

Garzón returned to his court to investigate the matter and in February 1995, Pérez Mariño resigned after publicly calling for González to do the same.

[3] Returning to the judiciary, Pérez Mariño sentenced the banker Mario Conde to six years in jail for his misappropriation of 600 million pesetas from the Banesto bank.

He quit his council seat and left politics for good in July 2005 for "strictly personal" reasons, returning to the judiciary; his party and the BNG then resumed their pact.