After unsuccessful electoral campaigns in Álava, Navarre, and Biscay, Bilbao competed in
1916 in the Carlist national stronghold, the
Gipuzkoan district of
Tolosa. He defeated the conservative candidate and became part of the 9-member Jaimist minority in the Cortes. In
1918, he ran again in the same district and was re-elected. Known for his active defense of the Church, religion, and Traditionalism, Bilbao distinguished himself as one of the most notable Carlist orators, though some critics described his style as having a penchant for purple rhetoric. During the
Mellista crisis, Bilbao remained loyal to the successive claimant,
Don Jaime, and worked closely with him, even editing some of his proclamations and documents. As the secession decimated the Jaimist ranks, Bilbao became the local Biscay jefe. In 1919, he was fielded as the provincial Jaimist candidate for the
Senate. Elected, he remained active, focusing on syndical laws and the autonomous status of universities. It is unclear why he abandoned his senatorial position in
1920 to run for the Cortes again, but this time, he returned to Navarre and was elected from another Carlist stronghold, the
Estella district. In
1923, during the last parliamentary campaign of the
Restoration, the Carlist king ordered abstention, and no official candidates were fielded. Though most Carlists initially welcomed the
Primo de Rivera coup, viewing it as a stepping stone toward a traditionalist, anti-democratic monarchy, their sympathy soon waned. Don Jaime eventually instructed his followers not to participate in the primoderiverista institutions. However, Bilbao ignored this directive and became one of the most vocal advocates of the dictatorship. In 1924, he joined the new state party,
Unión Patriótica. By 1926, he was appointed president of the Diputación de Bizkaia, a position he held for four years, during which he worked to negotiate the provincial
concierto económico. In 1927, he joined the newly appointed quasi-parliament, the
Asamblea Nacional Consultiva as a representative of the diputaciones provinciales. It is unclear which of these actions was the final straw, but Don Jaime and his political representative in Spain,
Marqués de Villores, remained firm and expelled Bilbao from the Carlist ranks. Despite this, Bilbao retained his Carlist identity and aligned himself with the Mellista branch of Traditionalism. He also remained active as a Catholic politician, heading the Biscay section of
Acción Católica from the early 1920s. He later participated in the first national congress and delivered an address. In 1929, he attempted to launch a new Catholic political grouping, but the initiative failed to gain traction, receiving only a lukewarm reception from the primate
Segura. During the
Dictablanda period, Bilbao reached out to the orphaned monarchist primoderiveristas from
Unión Monárquica Nacional, speaking at their public meetings. ==Republic==