On 19 June 1785 Rostocki was ordained by Primate of the Uniate Church
Jason Smogorzewski along with bishops Cyprian Stecki and John Kaczkowski as a bishop of Chelm. Earlier that year he also was confirmed as a coadjutor Metropolitan bishop of Kiev, Galicia and all Ruthenia.
Following the death of
Jason Smogorzewski, on 1 November 1788 he succeeded as the Metropolitan bishop of Kiev, Galicia, and all Ruthenia. In 1790 he resigned as bishop of Chelm. In 1796 Rostocki created Eparchy of Suprasl on territory of the
New East Prussia creation of which was approved by the Pope in couple of years.
He consecrated following bishops
Josaphat Bulhak, Porphyrius Skarbek Wazynski and Adrian Butrymowicz.
^The title is also known as the Metropolis of Kiev, Halych and all Rus' or Metropolis of Kyiv, Halychyna, and All-Rus'. The name "
Galicia" is a
Latinized form of
Halych, one of several regional principalities of the medieval state of
Kievan Rus'.