At first, it seemed that Przemysław had no better chance of getting any part of his father's inheritance; however, the early deaths of his older brothers Władysław (in 1355) and Bolesław (in 1356) made him the main heir of Duke Casimir I.

His marriage to Elisabeth, daughter of Bolesław, Duke of Koźle-Bytom in 1360 give him additional rights over the half of Bytom taken by his father Casimir I in 1357.

Przemysław quickly became one of the most important figures in the court of Prague, and Emperor Charles IV entrusted him with numerous (and sometimes very difficult) tasks.

[2] Przemysław also negotiated the marriage of Princess Anne of Bohemia, Charles IV's daughter, to Richard II, King of England.

In this new office, Przemysław's diplomatic skills were used in several disputes between various members of the local nobility, for example, in the peaces of Heidelberg and Koblenz and in 1389, during the negotiations about the borders between the Bohemian Kingdom and Meissen.

Przemysław's diplomatic efforts resulted in a treaty with King Władysław II Jagiełło of Poland, signed on 12 June 1397, where both sides pledged to fight banditry in the borderlands.

It was at this time that the Duke of Cieszyn became known by his nickname: Noszak (from Polish "nosić", to carry) The progressive disease forced Przemysław in 1396 to abandon his interference in Bohemian politics.

Finally, with the support of King Wenceslas IV, in 1384 he obtained half of both Głogów and Ścinawa and one year later (in 1385), he bought Strzelin to Duke Bolko III of Ziębice.

As the closest male relative of Duke Jan III of Oświęcim, Przemysław obtained the right of succession of his Duchy in case of his death without issue; in 1405, after Jan III's death, the Duke of Cieszyn inherited Oświęcim, but immediately he ceded them (with Zator) to his eldest son and namesake Przemysław, who one year before (in 1404) received the government of half of Głogów and half of Ścinawa.

Oświęcim was inherited by the late Duke's only son, Casimir, who, a minor at that time, was placed under the regency of his grandfather, and after his death, of his uncle Bolesław I, who received the independent rule of Bytom and Toszek in 1405.