The Diocese of Szombathely was founded by Queen Maria Theresa in 1777. The new diocese was formed from the territories carved out from the Győr, Veszprém and Zagreb Dioceses. The former Collegiate Chapter of Vasvár became its Cathedral Chapter. After the First World War, as a consequence of the Trianon Peace Treaty a part of the diocese got outside the Hungarian borders. From 1922 the Austrian parishes belonged to the Burgenland Apostolic Administration, then from 1960 to the Diocese of Kismarton (Eisenstadt). From 1923 a part of the Yugoslav (Muraköz) parishes was governed by the bishop of Maribor, another part by the bishop of Zagreb.
The older part of the Archives comes from the Cathedral Chapter of Vasvár-Szombathely, which preserved records from 1224. When due to the Turkish threat the Chapter of Vasvár was moved to Szombathely in 1578, its archives were placed in the tower of the castle church of Szombathely. At the end of the 18th century, when the cathedral had been completed, the archives of the chapter were placed in the room above the sacristy. The archival holdings were arranged several times. In the 1820s the material of the archives was divided into two groups. In the first group there were the records from before the end of the 17th century, put in chronological order, and in the second one the records arranged according to the estates. A list of the first group was drawn up by Canon Gyula Bertalanffy in 1910. The second group was arranged by retired county official Ignác Desics in 1894.
The material of the place of authentication (locus credibilis) was handled separately from the material of the “private archives”, and the “national” nature of the former one was emphasised by the statutes of the chapter. Thanks to this increased attention, the archives of the place of authentication were saved and removed from the city during the Second World War, so the records were not damaged during the bombing of the Cathedral on 4 March 1945. However, the private archives were seriously damaged. A lot of the records were destroyed and the surviving documents remained mixed for a long time, so the material became researchable only after the rearrangement of the archives in the 1980s. The material of the archives of the place of authentication was handed over to the territorially competent Szombathely State (today Vas County) Archives in 1958 and it has been preserved there ever since.
The records regarding the history of the diocese have been preserved in the Episcopal Archives since its foundation in 1777 but a few earlier records from 1556 onwards can be found here, too. Some of them were brought by János Szily from Győr and a lot of documents were handed over to the newly established diocese by the Archives of the Zagreb Archiepiscopate and the Veszprém Episcopate. The records kept in the archives in the bishop’s palace suffered material injury repeatedly over the centuries. During the Second World War the copies of registries were placed in the cellar and remained there for decades, where as a result of the moist air and water inrushes the bindings moulded and peeled off; some copies were destroyed. In 1992 the storerooms were renovated and extended. In 2000 a new research room was opened. In 2002 a new section was separated in the Dominican monastery to collect the archives of the parishes. Then in 2006 the archives moved out from the bishop’s palace and were transferred to the former canon’s palace, situated opposite to the cathedral.