During his chaotic reign, Bohemia became a pawn in the long German–Polish War between King Henry II and Duke Bolesław I, "the Brave", of Poland.

The eldest son of Duke Boleslaus II "the Pious", probably with his first wife Adiva, he succeeded to the Bohemian throne upon the death of his father in 999.

Boleslaus III turned out to be a weak ruler and soon entered into a fierce inheritance conflict with his younger brothers Jaromír and Oldřich.

By 1002, a revolt organized by nobles of the rival Vršovci clan (along with Boleslaus's son-in-law) forced him to flee to Germany, where he was received by Margrave Henry I of Austria.

Bolesław the Brave claimed the ducal throne for himself, invaded Bohemia in 1003 and took Prague without any serious opposition; he ruled as Duke Boleslaus IV for a little over a year.