The territory is divided into 25 parishes, located in the following sites: Oslo (3), Moss, Askim, Fredrikstad, Halden, Lillestrøm, Hamar, Kongsvinger, Lillehammer, Jessheim, Hønefoss, Stabekk, Drammen, Fagernes, Tønsberg, Larvik, Sandefjord, Porsgrunn, Arendal, Kristiansand, Stavanger, Haugesund and Bergen.

In 1537 - in the course of the Lutheran Reformation in Denmark-Norway and Holstein - Christian III of Denmark suppressed the Catholic episcopates at the Norwegian sees.

In 1834 the Catholic missions in Norway became part of the Apostolic Vicariate of Sweden, seated in the Swedish capital Stockholm.

On 26 February 2015, Norwegian authorities levelled charges of fraud against the Roman Catholic Diocese of Oslo and Bishop Bernt Ivar Eidsvig.

According to the charges, the diocese is under suspicion of registering people as members of the Roman Catholic Church in Norway without their knowing or consent and over the course of several years fraudulently claiming membership grants from the Norwegian government to the amount of 50 million kr.