Of noble birth, Stanislaus studied at Gniezno, Pol., and probably at Paris. While serving as canon and preacher at Kraków (Cracow), he was elected—after Pope Alexander II nominated him—bishop of Kraków in 1072. During that time Poland was in a state of political unrest, with active opposition to King Bolesław II the Bold. Stanislaus joined the opposition under the leadership of Władysław Herman, the king's brother, and excommunicated Bolesław.

In 1079 Stanislaus was accused of treason. The royal court found him guilty and sentenced him to dismemberment. Following the execution of Stanislaus, King Bolesław was forced to flee to Hungary. These events have remained a matter of controversy between those Polish historians who believe Stanislaus was part of a Bohemian-German plot designed to remove Bolesław and replace him with Władysław, and those who describe the execution as a contemptible act of revenge against a saintly bishop who had excommunicated a cruel, licentious king. In any case, miracles and legends spread the cult of the martyred bishop to Lithuania, Belorussia, and Ukraine, and Stanislaus became the patron saint of his native Poland.