An adept negotiator, he is also a prominent member of the Peruvian Aprista Party, serving in two occasions as the party's Secretary-General. As the right-hand man to the late former President Alan García, he served as his defense attorney during the first corruption and illicit enrichment allegations made in his first post-presidency, and finally as his first Prime Minister in his second presidency. After the "Petroaudios" scandal revealed Del Castillo's involvement, he tendered his resignation with the whole cabinet on October 10, 2008, to President Alan García, marking his political downfall.