Joseph Audo was a partisan of Mar Augustine Hindi and thus became an active opponent of Yohannan Hormizd: the strong conflict came to an end only through the direct intervention of two apostolic delegates sent by Rome in 1828–1829.

Joseph Audo was elected Patriarch of the Chaldean Church on July 28, 1847, and confirmed by Pope Pius IX on September 11, 1848.

Audo laid the foundations, with help from the Vatican, for the Chaldean Church to grow and flourish remarkably in the last decades before the First World War.

From his early days as bishop of ʿAmadiya, competing with the Nestorian church for the allegiance of the villages of the Sapna valley, he had appreciated the crucial role an educated clergy could play both in consolidating the Catholic faith where it already existed and in bringing it to new hearers.

In doing so he was following in the footsteps of Gabriel Dambo, whose revival of monasticism in the monastery of Rabban Hormizd in 1808 had been partly intended to supply the church with a well-educated and disciplined clergy.

To a certain extent it did; monks from the monastery were sent out as priests and deacons to Baghdad, Basra, and a number of Chaldean villages in the Mosul and ʿAmadiya districts in the 1820s, and no doubt served their congregations well.

Audo decided to replace it and in 1859, with financial assistance from the Vatican, built a new monastery of Notre Dame des Semences in a safer and more convenient site near Alqosh.

Despite the protests of the apostolic delegate at Mosul, Henri Amanton, Audo consecrated Thomas Rokos bishop of Basra and dispatched him to visit the Malabar Christians.

Meanwhile, Rokos, who had been excommunicated on the Vatican's orders by the vicar apostolic of Verapoly on his arrival in India, returned in failure to Baghdad in June 1862.

One of the members of the reunion which had given Rokos his mission, the metropolitan of Seert Peter Bar Tatar, refused to accept the censures carried by the delegate.

The Propaganda invoked the papacy's old privilege in such cases of directly appointing his successor, and asked the patriarch to submit three suitable names after discussion with his bishops.

As a result, in the 1870 First Vatican Council he was warmly welcomed as a member of the Church party opposed to the doctrine of papal infallibility, and joined in the opposition to the controversial constitution Pastor aeternus, absenting himself from the session at which it was promulgated.

He met the Sultan in Constantinople on 16 September 1870, and denounced the constitution as infringing on the traditional customs of the church and damaging the interests of the Ottoman empire.

In Quae in patriarchatu, a stinging encyclical of 16 November 1872 addressed to the bishops, clergy and faithful of the Chaldean Church, Pope Pius IX rehearsed the many examples of Audo's intransigence, deplored his disobedience and welcomed his eventual submission.

[6]: 740  His obituary was pronounced in a consistory held on 28 February 1879 by Pope Leo XIII, who praised him as "a man adorned with a fine sense of faith and belief" (quem eximius pietatis et religionis sensus ornabat).