| Jurisdiction: | Diocese |
| Graz-Seckau | |
| Latin: | Dioecesis Seccoviensis (Latin) |
| Local: | Diözese Graz-Seckau (German) |
| Coat: | Wappen Bistum Seckau.png |
| Country: |  Austria |
| Metropolitan: | Archdiocese of Salzburg |
| Territory: | Styria |
| Province: | Salzburg |
| Area Km2: | 16,392 |
| Population: | 1,240,214 |
| Population As Of: | 2019 |
| Catholics: | 817,000 |
| Catholics Percent: | 65.9 |
| Denomination: | Roman Catholic |
| Rite: | Roman Rite |
| Established: | June 22, 1218 |
| Cathedral: | Graz Cathedral |
| Patron: | Saint Rupert Saint Virgil |
| Bishop: | Wilhelm Krautwaschl |
| Metro Archbishop: | Franz Lackner |
| Emeritus Bishops: | Egon Kapellari |
| Map: | Bistuemer oesterreich graz.png |
| Website: | Website of the Diocese |
The Diocese of Graz-Seckau (Latin: Dioecesis Seccoviensis, German: Diözese Graz-Seckau) is a Latin Church diocese of the Catholic Church comprising the Austrian state of Styria. It is part of the Ecclesiastical Province of Salzburg.
The See of Seckau was founded on 22 June 1218, then the third suffragan of the metropolitan diocese of Salzburg after Gurk (1072) and Chiemsee (1215), by Archbishop Eberhard von Regensberg with permission from Pope Honorius III. Emperor Frederick II gave his consent on 26 October 1218; he conferred on the incumbent of the see the dignity of a Prince of the Roman Empire, though with no secular power. A fourth suffragan diocese, Lavant, followed in 1228.
The first bishop was Provost Karl von Friesach (1218–1230) who had his see at Seckau Abbey in Upper Styria; his diocese only comprised 13 parishes. Most of the time, the Seckau bishops resided at Seggau Castle near Leibnitz and at Graz, they also served as vicars in the Duchy of Styria. Under the Habsburg emperor Joseph II, the diocese was reorganised and its territory was enlarged. However, the original intention of the emperor to establish an archbishopric at Graz, the capital of Styria, was frustrated by the opposition of the Archbishop of Salzburg.
In 1786, the episcopal see was finally transferred from Seckau to Graz Cathedral, though the name of the diocese remained unchanged until 1963. A new cathedral chapter was installed, composed at first of three dignitaries and four canons. The see included thenceforth the Salzburg territory in Styria; at the same time, the short-lived Diocese of Leoben was created in Upper Styria. After the death of the first and only Bishop of Leoben, the administration of this see was again entrusted in 1808 to the Bishops of Seckau at Graz. The limits of Seckau are due to a regulation of 1859, incorporating the Diocese of Leoben into that of Seckau, while Seckau ceded Lower Styria with its (chiefly) Slovene-speaking population to the Diocese of Lavant with its see at Maribor (Marburg).
The diocese also operates a religious museum (Diözesanmuseum), housed in the former Jesuit University building in the Graz Old Town across from the cathedral and the Church of St. Catherine of Alexandria with the mausoleum of Emperor Ferdinand II.
The current bishop, Wilhelm Krautwaschl, was appointed by Pope Francis on April 16, 2015.[1]