[6] The other two thirds of the diocese were under the secular rule of the Teutonic Knights until 1525 and Ducal Prussia thereafter, both entities also being a protectorate and part of Poland from 1466.

Calvinist King Frederick II of Prussia confiscated the landed property of the Roman Catholic prince-bishopric and assigned it to the Kriegs- und Domänenkammer in Königsberg.

Along with Culm (Chełmno), Pomesania, and Samland (Sambia), Warmia was one of four dioceses in Prussia created in 1243 by the papal legate William of Modena.

After the Battle of Grunwald in 1410, the Sambian and Warmian bishops paid homage to King Władysław II Jagiełło of Poland and Lithuania, a maneuver to protect the territory from complete destruction.

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

[1] In the Second Peace of Thorn (1466) the Teutonic Knights renounced any claims to the Prince-Bishopric, and recognized Polish sovereignty over Warmia, which was confirmed to be part of Poland.

The bishops insisted on keeping their imperial privileges and ruled the territory as de facto prince-bishops although the Polish king did not share this point of view.

In the Second Treaty of Piotrków Trybunalski (7 December 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 native Prussians.

Renowned Polish astronomer Nicolaus Copernicus lived in the prince-bishopric, in the towns of Lidzbark, Olsztyn and Frombork, and there he began and completed his groundbreaking work on heliocentrism.

While nearly all of Ducal Prussia took on Lutheranism, the prince-bishops Stanislaus Hosius and Marcin Kromer and the Jesuits were instrumental in keeping much of the prince-episcopal Warmians Catholic.

Those new Catholic churches located in the ducal two thirds of Warmia diocese and in diocesan territory of the suppressed Samland see were then subordinated to the Warmian Frombork see.

This development was recognised by the Holy See in 1617 by de jure extending Warmia's jurisdiction over Samland's former diocesan territory, only containing few immigrated Catholics.