He was the oldest son of Duke Casimir of Bytom by his wife Helena. Despite his church career, in 1303 Bolesław received from his father the town of Toszek years duchy, which formally remained under his rule until his death (although the real government of that land, after Bolesław"s departure to Hungary, was performed by his younger brother Władysław).
Bolesław was designed by the father to the Church career, despite the fact that he was the eldest son. Already 1294 he was appointed Scholastic of Krakow, and three years later (in 1297), obtain the title of Canon of the Chapter of Wrocław. At the end of 1320, Bolesław went to the Krakow court, and at the beginning of the next year (1321) the King Charles I gave him the most important and powerful position of the Hungarian church: the Archbishopric of Esztergom.
During the first six years of his rule as Archbishop (1321-1326), Bolesław had to fight against extreme Franciscan faction, who at that time were considered too radical by Pope John XXII, trying to maintain their jurisdiction over Spisz, disputed by the Bishopric of Krakow (this conflict was only resolved after Bolesław"s death in 1332).
One of the greatest success of Bolesław during his rule was the normalization of the diplomatic relations between Hungary and Venice. These countries (who had a long-lasting dispute over the Adriatic coast), finally entered into an agreement after the Archbishop"s mediation: the rich cities of Dalmatia (who included Zadar and Split) were placed under Hungarian rule.
The local chapter was complete against the nepotism, but at the end, thanks to support of King Charles and Queen Elisabeth, the Archbishop obtain his purpose: in 1328 Mieszko was formally invested as Bishop. Bolesław died in December 1323 and was buried in the cathedral in Esztergom.
The Duchy of Toszek was then officially merged to Bytom by Duke Władysław.
