Royal Prussia (; or Preußen Königlichen Anteils) or Polish Prussia (Polish: Prusy Polskie; German: Polnisch-Preußen) was the denotation of those former districts of the State of the Teutonic Order including Pomerelia (Gdańsk Pomerania) with Danzig (Gdańsk), Chełmno Land (Kulmerland) with Michałowo Land and Toruń, the mouth of the Vistula with Elbląg and Marienburg (Malbork), and the Bishopric of Warmia (Ermland) with Allenstein (Olsztyn), which after the 1466 Second Peace of Thorn were ceded to the Kingdom of Poland. Until the 1569 Union of Lublin the region enjoyed a substantial autonomy. After 1569 it came under direct administration of the Crown of the Kingdom of Poland in the Polish-Lithuanian Commonwealth.
Administratively Royal Prussia was part of the Greater Poland Province together with Greater Poland proper, Masovia, and Łęczyca Voivodship and Sieradz Voivodship, with the Province capital being Poznań.
Before 1308 the Pomerelian part of the region, with Gdańsk, was part of the first Polish state, enjoying periods of autonomy and independence. During the rule of Władysław I the Elbow-high of Poland, the Margraviate of Brandenburg staked its claim on the territory in 1308, leading Władysław to request assistance from the Teutonic Knights, who evicted the Brandenburgers but took the area for themselves, annexed and incorporated it into the Teutonic Order state in 1309 (Teutonic takeover of Danzig (Gdańsk) and Treaty of Soldin). This event caused a long-lasting dispute between Poland and the Teutonic Order over the control of Gdańsk Pomerania. It resulted in a series of Polish–Teutonic Wars throughout 14th and 15th centuries. After their defeat at the Battle of Grunwald, the Teutonic Knights according to the 1411 Peace of Thorn had to pay large contributions to the Polish kings, which strongly affected the public budget. In view of rising taxes, several local nobles and Hanseatic cities in 1440 established the Prussian Confederation at Kwidzyn (Marienwerder) protesting against the Order's internal and financial policies. Grand Master Ludwig von Erlichshausen demanded the dissolution and in 1453 searched for help from Pope Nicholas V and Emperor Frederick III. In turn the Confederation declared the feud.
During the Thirteen Years' War ("War of the Cities"), in February 1454, the Confederation, led by the citizens of Gdańsk, Elbląg, and Toruń, as well as gentry from Chełmno Land sent a delegation with Johannes von Baysen to ask the Polish king for support against the Teutonic Order's rule and for incorporation of Prussia into the Polish kingdom. After negotiating the exact conditions of incorporation, the king agreed and delegates of the Prussian Confederation pledged allegiance to Casimir on 6 March 1454. King Casimir IV Jagiellon appointed Baysen as the first war-time governor of Royal Prussia.
The rebellion also included major cities from the eastern part of the Order's lands, such as Kneiphof (Knipawa), later a part of Königsberg. Though the Knights were victorious at the 1454 Battle of Chojnice, they were not able to finance further mercenaries in order to reconquer the castles occupied by the insurgents. Thirteen years of attrition warfare ended in October 1466 with the Second Peace of Toruń, which provided for the Order's cession to the Polish Crown of its rights over the western half of Prussia, including Pomerelia and the districts of Elbląg, Malbork, and Chełmno.
According to the 1454 Incorporation Statute issued by King Casimir IV, Royal Prussia enjoyed substantial autonomy as part of the Crown of Poland, it had its own treasury and monetary unit and armies. It was governed by a council, subordinate to the Polish king, whose members were chosen from local lords and wealthy citizens (ius indigenatus). Prussians had also seats provided for them in Polish Diet, but they chose not to use this right until the Union of Lublin. Toruń, Elbląg and Gdańsk (Danzig law) gained privileges similar to the status of a Free imperial city.
The Bishop of Warmia had claimed the title of an Imperial Prince-Bishopric status, as mentioned in the Golden Bull of 1356 by Emperor Charles IV. Although the area was never directly under the Emperor's jurisdiction and the claim seems unsupported by any bestowal document, it was in wide use in the 17th century. The bishopric continued defending this status until the end of the Holy Roman Empire in 1806.
The eastern part of Prussia remained under the rule of the Teutonic Knights and its successors as a fief of Poland, becoming the Ducal Prussia in 1525 when the Order's last Grand Master Albert von Hohenzollern adopted Lutheranism and secularized the land as its hereditary ruler. In 1618 the duchy was inherited by John Sigismund von Hohenzollern. It remained under Polish (and briefly Swedish) suzerainty and the rulers of Brandenburg had to swear – in the role as Prussian duke – formal allegiance to the Polish Crown. The dukes, in personal union electors of Brandenburg (vassals to the Holy Roman Emperor), achieved sovereignty for the duchy in the Treaty of Wehlau (1657).
As a result of the Union of Lublin in 1569, Royal Prussia's autonomy was abolished and the region was united with the Polish Crown. Prussian electors became senators and representatives to the Polish parliament, the Sejm. The region became part of the Greater Poland Province (prowincja wielkopolska) together with the former duchies of Greater Poland and Masovia, with the province capital at Poznań. The Prince-Bishopric of Warmia retained a certain grade of autonomy as a Polish protectorate.
The main task of the Sejmiks was the election of MPs for the Sejm of Poland. Royal Prussia was allocated 10 MPs (167 total).
During the First (1772) and Second (1793) Partitions of Poland, Royal Prussia was gradually annexed by the Kingdom of Prussia. Its territory largely made up the Province of West Prussia created in 1773.
In 1510, after several attempts to install another governor, the office was abolished.