After his father's death in 1306, Leszek succeeded him in the Duchy of Racibórz; but, because he was underage at that, he was placed under the regency of his uncle Mieszko I, Duke of Cieszyn until 1308.
On 19 February 1327, together with other Silesian rulers, Leszek paid homage to King John of Bohemia in Opava.
On 21 February 1334 Leszek increased his domains with the acquisition of the Duchy of Koźle by the amount of 4,000 pieces of silver from his cousin Duke Władysław of Bytom, with the compromise that, in the event of his death without issue, Koźle return to the Duchy of Bytom.
After his death, as a result of the arbitrary decision of King John of Bohemia (and despite the strong resistance of the other Piast rulers in Upper Silesia who were their closest male relatives), the Duchy of Racibórz was given to Duke Nicholas II, Duke of Opava, who claimed the rights of his wife Anna, Leszek's oldest sister.
Koźle returned to Duke Władysław of Bytom after the payment of a monetary compensation to Euphemia, Leszek's youngest sister.