He was the youngest son of Don Juan de Jasso y Atondo, Lord of Idocín, president of the Royal Council of the Kingdom of Navarre, and seneschal of the Castle of Xavier (a doctor in law by the University of Bologna, belonging to a prosperous noble family of Saint-Jean-Pied-de-Port, later privy counsellor and finance minister to King John III of Navarre) and Doña María de Azpilcueta y Aznárez, sole heiress to the Castle of Xavier (related to the theologian and philosopher Martín de Azpilcueta).