At the age of 15 Villanueva became a member of APRA's "Juventud Aprista Peruana" in opposition to the military dictatorship of Luis Miguel Sánchez Cerro. At the age of 18 he was imprisoned in El Frontón prison (located on the small island of "San Lorenzo" off the coast of Callao, Lima's main port) for his subversive activities in Peru. He was a political ally and personal friend of Víctor Raúl Haya de la Torre, the founder and most prominent leader of the APRA party.