From an early age he was prepared to take over the government in Masovia, alongside his older brother Janusz the Younger.
In 1409 he was sent by his father at the head of a retaliatory expedition against the Teutonic Order, culminating with the conquest and burning of Działdowo and 14 surrounding villages.
In 1414 he participated in another war with the Teutonic Knights, this time in person coordinating all the activities of the Masovian troops.
After 1422, following the death of his older brother, Bolesław received the district of Czersk, where he exercised his own court and government.
Around 1412,[2] Bolesław married the Lithuanian princess Anna (d. 25 May 1458 in Czersk), a daughter of Feodor Olgerdovich,[3] Prince of Rylsk, Ratnie and Bryansk, one of the eldest sons of Algirdas, Grand Duke of Lithuania, and in consequence, a half-brother of King Władysław II Jagiełło (born from Algirdas' second marriage).