The Diocese of Martirano was a Roman Catholic diocese located in the village and comune of Martirano in the province of Catanzaro in the Calabria region of Italy. It was suppressed in 1818 to the Diocese of Nicastro.
Paul Fridolin Kehr draws attention to a group of bishops who are attested between 649 and 769 and identified as bishops of Martirano in the Italia Sacra of Ferdinand Ughelli: Reparatus, Opportunus, Domnus and Bonus. Inspection of the evidence shows that these bishops belonged to the diocese of Manturano in Tuscany, not Martirano in Calabria. Francesco Lanzoni likewise rejects Reparatus as a bishop of Martirano. These bishops cannot be used to argue for an early establishment of the diocese. Ughelli also reports that Arnulphus was a bishop of Martirano, citing William of Tyre's story of his attempting to intrude himself into the Patriarchate of Jerusalem. But William of Tyre does not say that Arnulphus was Bishop of Martirano c. 1100; it is only a conjecture of Ughelli. Ughelli also reports the existence of a Bishop Rodulphus under Pope Calixtus II, but the documents on which the report is based are forgeries.
It is said that the Diocese of Martirano was established in 1099. Louis Duchesne states that Martirano had been a suffragan of Salerno in 1058, and that Martirano may have replaced the Byzantine Greek diocese of Amantea.
In 1638 a major earthquake struck Calabria. At Martirano the death toll was 517, and most of the town was destroyed. The cathedral could not be repaired, and Bishop Cellesio had to begin building a new one.
The Cathedral was served by a Chapter, composed of four dignities (the Dean, the Archdeacon, the Cantor and the Treasurer) and eight Canons. Bishop Pierbenedetti added six chaplains. All were required to be in priestly orders. In 1703 the number of Canons was twelve.
Bishop Marino Pierbenedetti (1577–1591) was also responsible for the building of the seminary in Martirano, in accordance with the decrees of the Council of Trent and the active encouragement of Bishop Gaspare del Fosso, Archbishop of Reggio and Metropolitan of Calabria.
On 27 June 1818 the diocese of Martirano was suppressed and its territory was added to that of the Diocese of Nicastro, in accordance with the Bull In ultilori of Pope Pius VII. This was in conformity with the Concordat of 1818, between the Holy See and the Kingdom of the Two Sicilies.