He was the first president of the Provisional Government of the Basque Country and the executive defense advisor during the Spanish Civil War.

He later took responsibility for the business and introduced many reforms, including free health care and paid holidays, which significantly improved conditions for the workers in the factory.

In 1931 and 1932, Aguirre intervened decisively in failed attempts at Basque devolution, which called for self-government, including in Navarre.

On 5 November 1933, two weeks before a general election, a referendum was held in Álava, Gipuzkoa and Biscay on new wording for the Statute of Devolution, which abandoned the inclusion of Navarre.

[4] As a result of the dissolution of the legislature for the general election, the hesitation of radical government,[5] and Carlist opposition to the incorporation of Álava in the statutory process,[6] devolution was prevented until 1 October 1936, when the Spanish Civil War started.

After a religious ceremony at the Basilica of Begoña in which he swore allegiance to Catholicism, his country and his party, he visited Gernika and took his oath of office in the Basque language: Jainkoaren aurrean apalik, Eusko Lur gainean zutunik, asaben gomutaz, Gernikako Zuhaizpean, herri ordezkarion aintzinean nere agindua ondo betetzea zin dagit.

[7] English translation: "Humble in front of God, Standing in our Basque lands, Remembering our heritage, under Gernika's venerable tree, as president of my country, I swear to serve my term faithfully."

Oath of Office, 17 September 1936A government of conciliation was formed by Basque Nationalists, Socialists, Communists, and other Republicans but not without tensions among them.

[9] In June 1937, the Franco's Nationalists broke through the Iron Ring of Bilbao and entered the city as a result of the treachery of Alejandro Goikoetxea, the engineer who had designed the fortifications.

Agirre moved his government to Trucíos before he headed to Santander and finally to Catalonia, where he prepared to continue fighting with his men.

Despite intense efforts made by Manuel de Ynchausti in the United States, Aguirre's true identity was in danger of being discovered within a month.

He wrote then to Ramón María de Aldasoro, the former trade and business secretary of the Basque government, who led the Euzkadi delegation in Buenos Aires, Argentina.

The Uruguayan president, General Alfredo Baldomir, agreed, and he even received Aguirre with honours in accordance with his status.

Aguirre decided to place the large Basque exiles' network at the service of the Allies, and collaborated with the US Secretary of State and the CIA to defeat their common enemies.

His body was shipped from Paris to Saint-Jean-de-Luz in the French Basque Country, where it spent a night in the Monzón house and was buried on 28 March after a funeral Mass at the Saint-Jean parish church.