The Archcathedral Basilica of the Assumption of the Blessed Virgin Mary and St. Andrew in Frombork is listed as a Historic Monument of Poland.

By the double function of prince-bishops they officiated as spiritual leader in the diocese and as secular prince in the Prince-Bishopric of Warmia, a semi-independent state comprising about a third of the actual diocesan territory, first as part of Teutonic Prussia.

During the war Warmia was partly recaptured by the Teutonic Knights, however, in 1464 Bishop Paweł Legendorf vel Mgowski sided with Poland and the Prince-Bishopric came again under the overlordship of the Polish King.

When King Casimir IV attempted to reduce the prince-episcopal autonomy this caused the War of the Priests.

Prince-Bishop Lucas Watzenrode, officiating between 1489 and 1512, aimed at Warmia's exemption from Riga in order to establish a Warmian metropolis, comprising the dioceses within Teutonic Prussia, part of Poland as a fief since 1466,[6] as suffragans.

In the Second Treaty of Piotrków Trybunalski (December 7, 1512) Warmia conceded to King Alexander Jagiellon a limited right to propose four candidates to the chapter for the election, who however had to be residents of the province of Royal Prussia.

Following King Sigismund III's Prussian regency contract (1605) with Joachim Frederick of Brandenburg, and his Prussian enfeoffment contract (1611) with John Sigismund of Brandenburg these two rulers guaranteed free practice of Catholic religion in all of prevailingly Lutheran Ducal Prussia, a vassal duchy of Poland.

But based on these contracts the prince-bishops gradually extended their de facto competence beyond the territory of their proper prince-bishopric of secular rule.

This development was recognised by the Holy See in 1617 by de jure extending Warmia's jurisdiction over Sambia's former diocesan territory.

In 1930 the diocesan exemption ended and Ermland, then led by Bishop Maximilian Kaller, became part of the Eastern German Ecclesiastical Province under the newly elevated Archdiocese of Breslau (Wrocław).

Following the defeat of Germany in World War II, Warmia became again part of Poland, although with a Soviet-installed communist regime, which stayed in power until the Fall of Communism in the 1980s.

August Hlond had appointed Teodor Bensch as Apostolic Administrator superseding the still existing capitular canons, who otherwise could have elected a new bishop candidate.