The duchy was formed after gaining independence from the Kingdom of Poland in the 11th century, following the death of Bolesław I the Brave in 1025.

In 1210, it briefly became a fiefdom of Denmark under the rule of Valdemar II, until it was reconquered the next year by the king of Poland, Leszek the White.

[5] According to Józef Spors, despite some cultural differences, the inhabitants of the whole of Pomerania had very close ties with residents of other Piast provinces,[6] from which Pomerelia was separated by large stretches of woodlands and swamps.

[7] In the eleventh century the region had loosened its close connections with the kingdom of Poland and subsequently for some years formed an independent duchy.

[10] A campaign by Piast duke Władysław I Herman to conquer Pomerelia in 1090–91 was unsuccessful, but resulted in the burning of many Pomerelian forts during the retreat.

[4] In 1116, direct control over Pomerelia was reestablished by Bolesław III Wrymouth of Poland,[11] who by 1122 had also conquered the central and western parts of Pomerania.

[12] While the latter regions (forming the Duchy of Pomerania) regained independence quickly, Pomerelia remained within the Polish realm.

The principes in Pomerelia gradually gained more local power, evolving into semi-independent entities, much like other fragmented Polish territories, with the difference that the other parts of the realm were governed by Piast descendants of Bolesław III.

[17] Peace was restored only in the Treaty of Christburg (Dzierzgoń) in 1249, mediated by the later pope Urban IV, then papal legate and archidiacone of Lüttich (Liege).

[18] In this conflict, Swietopelk II initially won the upper hand, but could not force a final decision.

[14] These brothers initiated another civil war, with Mestwin II allying with and pledging allegiance to the Brandenburg margraves (Treaty of Arnswalde/Choszczno 1269).

Władysław, sold his rights to the Duchy of Kraków to King Wenceslaus II of Bohemia in 1297 and accepted him as his suzerain in 1299.

This event caused a long-lasting dispute between Poland and the Teutonic Order over the control of Gdańsk Pomerania.