From 1911 to 1914 he served as the personal aide to the Bishop of Gherla (his uncle Vasile) and became friends with Prime Minister István Tisza.

The death of his cousin prompted him to join as a chaplain so the new lieutenant left in December 1914 from Timișoara to Vienna where he tended to the soldiers.

In November 1918 Hossu was nominated representative by right in the National Assembly of all Romanians in Hungary, which declared the Union of Transylvania with Romania on 1 December 1918.

[2] On 1 December 1918 Hossu read the Resolution of the National Assembly in front of the crowds gathered in Alba Iulia, preceding it with the following words: "Brethren, the hour of fulfillment is this one, when God Almighty is speaking out His centuries-old longing for justice through His faithful people.

[3] Next day, at Iuliu Maniu's proposal, the High National Romanian Council mandated representatives Vasile Goldiș, Alexandru Vaida-Voevod, Iuliu Hossu, and Miron Cristea to go to King Ferdinand I and present him with the Resolution of the National Assembly.

[5] On 1 October 1948 he gave an Exclamation Decree (ipso facto) to the participants in the Cluj Assembly of the 36 Greek Catholic priests who would decide to break the Greek-Catholic union with the Church of Rome.

Both the communist authorities and the leadership of the Romanian Orthodox Church represented by Patriarch Justinian Marina personally offered him the Orthodox metropolitan chair of Moldavia in exchange for renouncing the Catholic faith and the connection with Rome and Catholic Church.

Following the Greek-Catholic Liturgy celebrated at the Church of the Piarists in Cluj on 12 August 1956 by the three united bishops alive at the time, they were dispersed from Ciorogârla.

During his forced domicile at Ciorogârla Monastery, Hossu was regularly visited by Orthodox hierarchs, including Justinian Marina, Teoctist Arăpașu and Gherasim Cristea.

According to the memoirs of the Greek-Catholic priest Ioan Mitrofan, Andrei Andreicuţ was also among those who visited Hossu in Căldărușani.

[7] On 28 April 1969 he was created a cardinal but Pope Paul VI reserved Hossu in pectore (to be kept secret).

On 22 February 1969 the pope had granted a private audience to Hieronymus Menges and the prelate asked Paul VI to do something that would encourage the faithful and give them a sign that the Romanian people were close to his heart.

The prelate then recommended that the pope raise Hossu and future Servant of God Áron Márton as cardinals and to appoint some priests as monsignors.

[8] Archbishop Agostino Casaroli sent his aide not long after this to Bucharest to ask the Minister for Culture whether or not the government would accept the two promotions.

The beatification process – which conferred the title Servant of God upon him – commenced with the declaration of "nihil obstat" (nothing against) to the cause on 28 January 1997.