It was founded on 28 January 1785[1] but after the death in 1800 of its first and only bishop, its incorporation into the Diocese of Seckau was ordered in 1804 by Holy Roman Emperor Francis II.
The Diocese of Leoben was created at the wish of Holy Roman Emperor Joseph II, who was also Archduke of Austria, from territory belonging to the Archdiocese of Salzburg.
Pope Pius VI gave his consent to its creation on 17 March 1786.
[1] The episcopal seat was in the church of the former Göss Abbey near Leoben, where a cathedral chapter was set up.
The diocesan territory comprised the districts of Bruck an der Mur and Judenburg together with the area round Aussee, and contained 157 parishes.