In March 1241 he succeeded his uncle as Voivode of Kraków after the death of Włodzimierz at the Battle of Chmielnik.

Kraków was sacked a week later by an army of the Mongol empire during their first invasion of Poland, culminating in the Battle of Legnica where his father Sulisław and most of the Polish high nobility, including Henry II the Pious, were killed.

members of the Sarmatian Zych (Záh) clan, with the aim of putting Bolesław Wstydliwy on the throne of Kraków.

After this victory Bolesław took control of Kraków, a move supported by Bishop Jan Prandota.

Klement rebuilt the Będzin Castle (near Zagórze and Klimontów) and a Zych garrison protecting the silver mines of Rosperk was placed at nearby Zychcych (Żychcice).