Son of Kazimierz II the Just and Olena Vsevolodivna, daughter of Belz Prince Vsevolod Mstyslavych (according to another version, of Rostyslav Mstyslavych, Prince of Smolensk and Kyiv).
After the death of his father in 1194 he lost the Krakow Duchy, which he managed to return with the assistance of the clergy. He had to give away Mazovia and Kujavia to his brother Duke Konrad of Mazovia.
In 1195 Leszek got the assistance from Roman Mstyslavych at the battle of the River Mozgawa against Mieszko III the Old. In 1199 he helped Roman Mstyslavych to capture Halych lands. In 1205 a military conflict developed between Roman Mstyslavych and Leszek I the White and Konrad of Mazovia. At the battle of Zawichost Polish troops defeated Halych army and Roman Mstyslavych died.
In 1214 at Spiš (Slovakia, north of the then Kingdom of Hungary) an agreement was concluded with Hungarian King András II, according to which Hungarian King Koloman
He died at Gąsawa, during the campaign against DukeŚwiętopelk II of Eastern Pomerania, and was buried in Krakow. His wife was Hremyslava Inhvarivna from Lutsk. He had two children: Salome (married to King Koloman of Hungary) and son Boleslaw (known as Boleslaw the Chaste; with time succeeded his father on the Krakow throne.
Portrait (imaginary) of Leszek I the White