[4] According to a tradition unsupported by evidence, Ivrea is the place where Saint Patrick was consecrated bishop, c. 431, before evangelizing Ireland.

Blessed Thaddeus MacCarthy died here in 1492 as a pilgrim returning from Rome to Munster, Ireland and miracles hae been attributed to him.

[8] Bishop Enrico (1029–1059) was the founder of the monastery of Saint Stephen in the diocese of Ivrea in 1044, for which he obtained papal confirmation after the Roman Synod in 1059.

The Pope ordered that, if he did not resign voluntarily, seeing that charges of simony and neglect (dilapidatione ac symonia) had been proven, they were to depose him.

On 26 October 1206 the Pope replied, urging him to return to Ivrea, pointing out that a bishop is married to his church and ought not to desert his obligations to his spouse.

The Emperor Otto IV (1209–1215) had appointed a Rector of Ivrea, Guido di Biandrate, which was renewed by Frederick II on 20 May 1238.

Finally, in 1248, Frederick gave Ivrea and Canavese to Thomas II, Count of Savoy, though the transfer did not take effect due to the death of the Emperor.

The appointment of procurators who never were consecrated bishops, Conradus (1243–1249) and Fredericus de Fronte (1264–1289), and a bishop, Joannes de Barono (1250–1264), who was not consecrated until six years after his appointment,[13] meant long years without strong leadership, until finally, in 1313, Emperor Henry VII made Ivrea a subject of the Counts of Savoy.

[15] In June 1630, a major outbreak of plague struck the area of Ivrea, in the wake of the French invasion of Louis XIII.

King Victor Amadeus died on 18 October 1796, and his son and successor, Carlo Emanuele was forced to abdicate on 6 December 1798.

As in metropolitan France, the government program also included reducing the number of bishoprics, making them conform as far as possible with the civil administration's "departments".

When Bonaparte crossed the Alps again in the Spring of 1800, intent on driving the Austrians out of the Po Valley, he sent General Jean Lannes to secure Ivrea and destroy its fortifications.

[24] The confused situation of the dioceses in Piedmont was addressed by Pope Pius VII in his bull Beati Petri (17 July 1817)[25] as far as the redrawing of diocesan boundaries was concerned.

[29] In an Imperial Decree of 6 May 1806, the Emperor Bonaparte ordered that the Chapter of Ivrea consolidate all of the property of its prebends into a single fund, and apportion the dividends to each of the Canons on an equal basis.

In a decree of 8 May 1806, he consolidated (i.e. suppressed) the Collegiate Churches of Castelnuovo di Scrivia, Csteggio, Cavaglià, Livorno, Masserano, and S. Benigno, uniting them with the Cathedral.

[31] The carved walnut reredos depicting motifs of plants and human and animal figures, attributed to Baldino of Surso, are now in the Civic Museum of Ancient Art in Turin.

On the foundation pillar of the southern bell tower, a holy warrior is depicted, possibly representing a member of the Theban Legion.