Twenty-three months later (9 November 1301), the unexpected death of his father left Bernard as ruler of all his domains, together with his younger brothers Henry I and Bolko II as co-rulers.

However, because the three princes are minors, their guardianship was taken over by their maternal uncle Herman, Margrave of Brandenburg-Salzwedel, who also held the regency of the Duchy until 1305, when Bernard was proclaimed an adult and took by himself the government and the custody of his brothers.

The marriage of his sister Beatrix to Duke Louis IV of Bavaria (later German King and Holy Roman Emperor) in 1308 give Bernard a powerful alliance.

In 1311 Bernard took part in the negotiations in Olomouc as a mediator between Duke Bolesław III the Generous of Legnica and King John of Bohemia for the possession of the Duchy of Opawa (Troppau).

His effective government helped to increase the power of his Duchy, which allowed his son Bolko II to become the last (and most notorious) independent ruler of the Piast dynasty.