He is best known as author of Historia del Carlismo (1939), for half a century a key reference work on history of Carlism and today considered the classic lecture of Traditionalist historiography.

His father, Juan Miguel Oyarzun Seminario (1856–1908),[3] ran a petty rural merchant business; though in the 1890s struggling when transporting goods on his mules across the hostile terrain,[4] in the early 20th century he was already operating a few shops.

[6] It seems that they were brought up in a fervently Catholic, militant ambience, perhaps flavored by Integrism; in the early 1890s the parents and children alike are recorded as signing up various letters, e.g. protesting reported mistreatment of the Pope, and printed later in an Integrist newspaper El Siglo Futuro.

[19] Román Oyarzun Iñarra served as alférez provisional in the requeté Tercio de Zarate;[20] he and his brother Francisco Javier[21] joined Ministry of Foreign Affairs during the early Francoist era[22] and held various posts in Spanish diplomatic service, assigned to missions across the world though mostly in Latin America.

[29] When back in Pamplona he engaged in party initiatives; apparently considered an erudite, he was entrusted with delivering addresses to local audience, e.g. during opening of a new city círculo in 1906.

[38] In 1910 the Vascongadas party tycoon, Tirso de Olázabal, first advised and then "almost forced" Oyarzun to visit the exiled Carlist king, Don Jaime, in his Frohsdorf residence.

[39] The purpose quoted was to gather information for a booklet,[40] though it is also possible that following earlier resignations of Juan Vázquez de Mella and Antero Samaniego,[41] Don Jaime was looking for their successor as his personal secretary.

[52] Assuring his king that he was ready to abandon public duties any moment should the need to "conquistar el trono español" arise,[53] later that year he entered the Spanish consular corps[54] and in 1912 was already vice-consul in Liverpool,[55] holding the post also in 1913[56] and 1914.

He set up a company, named Alpha S.A., which dealt in import and sales of specialized machinery; it opened premises at prestigious locations in Madrid, but also in Barcelona, Valencia, Bilbao, Cadiz, Zaragoza and Vigo.

[71] Another milestone step was made in 1932, when near Atocha he moved into a 14,000 square meters building, serving also as an assembly plant;[72] at that stage the company was active also in Portugal and Northern Africa.

[73] In parallel to already stable and prosperous business, in January 1931 Oyarzun applied for resumption of consular service and was admitted as agregado commercial de segunda clase.

[77] In particular, it is not known whether Oyarzun was still in London when in 1934 he was appointed to Vienna, promoted to first secretary of the Spanish legacy and accepting his already customary post of commercial attaché, territorially covering Austria, Hungary and Czechoslovakia.

[90] Until some time in 1937 he believed in birth of a foral corporative regime,[91] yet also following the Unification Decree he remained entirely loyal to the emerging Francoist system and occasionally published pieces looking like a praise of Carlist identity within the new national conglomerate.

[105] Priding himself on cool matter-of-fact analysis, he considered the monarchist idea in decline[106] with the throne vacant and no appropriate candidate,[107] yet in 1965 he bothered to publish a work intended to counter the Juanista propaganda.

The first incursion into the area was a 1935 translation from English, Campaña de doce meses en Navarra y las Provincias Vascongadas con el general Zumalacárregui.

[118] Oyarzun's proposal, originally to be titled Compendio de Historia del Carlismo,[119] immediately replaced outdated Pirala's work as the first reference book on history of Carlism, the position it would occupy itself for the next half of a century.

[121] Belligerent threads aside Oyarzun is concerned primarily with politics, much attention dedicated also to personalities and some to the doctrine; social transformations and economic issues are generally treated marginally.

Since the author ignores non-Carlist Traditionalism the book tends to emphasize the dynastic question as the backbone of Carlism, especially that with the death of Alfonso Carlos he considers the Carlist history to be over.

[125] Historia del Carlismo was welcome by scholars[126] and the public alike as certified by numerous re-editions, especially that the narrative ended conveniently in 1936 and did not pose a challenge to the official Francoist propaganda.

Until the 1990s it remained the key concise volume on Carlist history, with an alternative offered only by massive and detailed series of Melchor Ferrer, appearing between the early 1940s and the late 1970s.

[155] His perceived pride in technocratic, no-nonsense "let’s get real" stand was deemed responsible for excessive and unfair challenge on allegedly spiritual and romantic nature of Carlism[clarification needed].

[158] Apart from customary charges related to bias, the other ones raised most often are insufficient source criticism,[159] overfocus on dynastic issues[160] and military history,[161] entanglement in juridical hair-splitting,[162] ignorance as to the social dimension,[163] downplaying religious issues,[164] failure to investigate the link to peripheral nationalisms,[165] factual errors,[166] reducing internal debates and secessions to personal squabbles,[167] unduly emphasis – bordering obsession[168] - on the Integrist thread[169] and rejection of menendezpelayista perspective of examining the cultural fabric.