The lordship was ruled by a single family, the House of Guevara (in Basque, Gebara), who all hailed from the town with the same name in Álava.

Their titles as Lords of Oñati were first conferred by the monarchs of Navarre, as the Lordship acted as a vassal state of the former.

The lordship is mentioned for the first time in a text from 1284, although some latter documents (dated in the 15th century) state that the majorat over the land around Oñati was given to the Guevara family in the year 1149.

The family had important contacts with the Navarrese monarchy and had been supporters of the Gamboino faction during the War of the Bands.

[2] In the year 1481, the Catholic Monarchs confirmed the lands and title as Count of Oñate to Íñigo Vélez of Guevara and Ayala, 13th Lord of Oñate-[3] The Lordship of Oñate was dissolved and the title lost when Oñati was officially incorporated into the province of Gipuzkoa as a town in 1845.