He was the third son of Bolesław II the Bald, Duke of Legnica by his first wife Hedwig, daughter of Henry I, Count of Anhalt.

Bernard actively supported the policy of his father Bolesław II and his brothers, Henry V the Fat and Bolko I the Strict (for example, he participated in the victorious Battle of Stolec).

After the death of his father in 1278, Henry V gave his younger brothers Bernard and Bolko I the Duchies of Lwówek (Löwenberg) and Jawor as co-rulers.

Little is known about this period in Bernard's life, and the only certain fact was (according to the chronicles), that he promoted and protected knights, a common practice among medieval princes.

Lwówek had a special gratitude to him after he supported the Silesian monastery of the Knights Hospitaller, where he was a generous benefactor, giving them among other things in 1281, the village of Cieplice [pl].