He studied at the Jesuit College of Orduna, where he graduated from high school in 1907. In 1910 he graduated from the Faculty of Philosophy and Arts at the University of Deusto and in 1912 he also graduated from the Law faculty of the same university. In 1916 he married Aurelia Pozueta Aristizabal, with whom he had a daughter, Miren. His wife died in 1918.
He was Foral Deputy of Nabarra in 1921 and 1930. Member of Parliament for Giipúzkoa in the elections of 1931, 1933 and 1936. In 1936 he defended his party's position in favor of the Second Republic and against the military uprising.
Between September 1936 and May 1937 he was minister without portfolio in the Government of Largo Caballero with the function of trying to restore the functioning of an elementary justice system in the Republican zone. This function continued as Minister of Justice in Negrin's government until December 1937. He left office, among other reasons, due to the government repression carried out against the Worker;s Party of Marxist Unification (POUM), but remained as minister without portfolio until August 1938. After the Spanish Civil War he was exiled in the UK. Following the changing position of the PNV, as collaborator with the rest of Spanish exile members during the War and after the War. He created and chaired the National Council of Euskadi between 1940 and 1942 and was minister of the Republican government in exile (1945-1947) . Thanks to his work in building Europe in 1972 was appointed honorary president of the Federal Council of the Peninsula for the European Movement.
He returned to Spain in 1977, the year he was elected senator of Nabarra from the Autonomic election lists. In 1979 he was elected to the Provincial Parliament of Nabarra as head of the list of the Basque Nationalist coalition, its first president.
Author, among other works, of England and the Basques and Basque Political Institutions (1945)..
Irujo wrote the following Decalogue, which summarizes his ideology:
1) I do declare and affirm that I am Nabarran by birth and heart, and therefore Basque, as Gipuzkoak, Arabakoak, Bizkaikoak, Lapurdikoak and Xiberokoak.
2) That my country is Nabarra, formerly called Baskonia, the only and truly homeland of all Basques.
3) That being Basque, i am not Spaniard nor French, but only Nabarran national..
4) That I am ethnically and culturally Basque, not Spaniard nor French.
5) That my natural language is Euskara, the so called Lingua Navarrorum by Sancho the Wise, not French nor Spanish.
6) That as Nabarran, I do want, claim and demand the sovereignty of Nabarra without interference or custody of any other country.
7) That as a progress abdicate Nabarran, I wish for my country to belong to the Confederation of the European Union.
8) That as truly patriotic love my culture, claim that the glorious history of this country be taught in all schools. That the use and implementation of our language, laws, culture be established and protected in our institutions. And that the sacred human rights of each person be always respected.
9) That all our natural resources and landmarks be common cultural heritage of all Nabarrans, and may all have free access to any level of education.
10) That Nabarrans of all social classes have access to wealth and general welfare in our country, without distinctions nor restrictions, respecting our Fores and Freedom.
Without doubt Mr.Irujo was an authentic Pyrenean, whose Nabarran patriotism guided him to know exactly the contents of the Pyrenean Law common to the whole Pyrenean isthmus, and how to put them in practice.
