His career climaxed during last decades of the Restoration period: in 1903 he was elected to Congreso de los Diputados, the lower chamber of the Cortes, and in 1905, 1916 and 1918 he was voted into the Senate.

The surname of Arana has been recorded already in the Medieval period, but ancestors of Teodoro can be traced back only to the early 18th century; his great-great-grandfather, born in 1703, was the native of the Biscay town of Arteaga.

[7] At unspecified time, probably in the mid-19th century, Arana Torrezuri married María Dolores de Beláustegui Arriaga from Busturia, also a town at the Oca banks.

The first information identified is from 1887, when Teodoro was nominated juzgado de primera instancia in Guadix; however, he resigned this position[15] and in 1890 latest was noted as engaged in law practice in Guernica.

[19] The marriage elevated Arana to high-bourgeoisie and dramatically changed his financial position; in Guernica the couple built an imposing palace-like family residence, named Nere Kabia.

[29] There is no information available on political preferences of more distant Arana's ancestors; his father was of Traditionalist inclinations and in the 1860s all family members – including the 7-year-old Teodoro – were listed in a Carlist periodical as donating money to religious cause.

[30] In 1873 his older brother Joaquín as a 19-year-old volunteered to legitimist troops,[31] but there is no information that Teodoro – in his late teens during last years of the Third Carlist War – followed suit.

[32] In 1885 he was noted as a signatory of open letters, published in the press in support of the then top Carlist theorist, Ramón Nocedal,[33] but he did not follow the Nocedalistas during the 1888 breakup.

[43] Before the Congress’ term expired in 1905 Arana barely made himself visible, noted only for an initiative to raise benefits for rural parochial clergy[44] and for signing some motions, e.g. the one on military issues by a fellow Carlist Llorens.

[54] During his electoral campaign Arana published an opened letter, titled A los carlistas guipuzcoanos; he claimed that objectives of the League overlap with the Carlist ones and defended his access to the alliance.

The liberal press cheered upon perceived "descomposición del carlismo", but the Basque regional jefe Tirso de Olazabal limited himself to publishing an ambiguous letter.

[59] Another thread of his activity was engagement against so-called Ley de Jurisdicciones, which declared some sort of offences under the military jurisdiction;[60] his address in the chamber was later published as a pamphlet.

[67] At some point the Carlist national leader, marqués de Cerralbo, asked Arana to enter the 3-member directorio, a provisional party board supposed to introduce discipline.

His campaign was aimed mostly against a faction identified as "piñosos", those suspected of sympathy towards La Piña;[71] it was an informal liberal grouping led by Víctor Chávarri, which dominated Biscay politics of the period.

[72] Arana claimed that "levadura rebelde" bewildered "gran parte de la masa del Partido";[73] he issued Reglamento, unheard of before,[74] called for unity behind the "Dios, Fueros, Patria, Rey" theme[75] and declared war against "modernismo político".

[85] It declared autonomy as "medio transitorio" on the path towards the future foral system end called all parties operational in Vascongadas to join common efforts to get it restored.

[90] In early 1919 the Biscay Junta Señorial declared that they were not obliged to follow recommendations from the Madrid headquarters; Arana issued a manifesto which voiced both against designs of "Estado Vasco" on the one hand and against "régimen centralista y opresor" on another.

[91] The conflict seemed solved when Jaime III returned from wartime house arrest in Austria and dissolved the central executive, result of the long-standing fray with the Mellistas.

[95] The volume is divided into 2 parts: the first, titled En justa defensa, is a partisan account of political turmoil within the Biscay branch of Carlism throughout the previous decade; Arana defends himself against charges of sustaining separatism.

[97] The second part, titled La cuestión foral, is a call to restore separate Basque legal establishments, symbolised by the Guernica oak and abolished during the 19th century.

The key motive listed behind the publication is countering "criminal campaign" against Biscay liberties, pursued by "malos vascos" who call themselves Traditionalists; they joined "planes maquiavélicos" and propaganda "anti-patriotica, anti-fuerista, anti-vasca y, sobre todo, anti-vizcaina".

He pictures Basques as a "separate nation"[106] or even "raza vasca" (terms avoided by Echave),[107] even though he declares them "dentro de la unidad nacional española".

Arana's activity as the local Carlist leader in Biscay was reduced to delivering addresses during religious rallies flavored with Traditionalism (e.g. in 1924 in Begoña),[116] to attending commemorative events related to Third Carlist War (e.g. in 1925 in Guernica),[117] to presiding over close banquets (e.g. in 1926 in Bilbao),[118] to donating money for related causes (e.g. in 1927 during Fiesta del Diario Jaimista),[119] to homage meetings (e.g. in 1928 in Barcelona to honor Miguel Junyent)[120] or to speaking at Jaimista círculos (e.g. in 1929 in Vitoria).

[122] He also intended to build a 4-floor health resort at Playa de Laga (Ibarranguelu), where he had earlier bought a plot of some 7 hectares,[123] but these plans eventually came to naught.

[129] He maintained close links with the new Madrid Carlist periodical, El Cruzado Español, which repeatedly hailed him as a Traditionalist patriarch and featured his photo on its pages.

His Nere Kabia residence, due to its large size and solid construction, was turned into one of the city shelters, supposed to accommodate people seeking refuge during air raids.

[144] The Nere Kabia palace has not been rebuilt, and today merely the street name marks the place where it used to stand, though at least until the late 20th century numerous plots and estates in the neighborhood still remained in hands of Arana's descendants.