[citation needed] As a child, Leo took part in the Battle of Jarosław, in which his father defeated the coalition of prince Rostislav Mikhailovich, a pretender to Galician throne, and returned control over Halych.

[3] After inheriting the Galician throne upon the death of Daniel in 1264, Leo moved the principality's capital from Halych to the newly founded city of Lviv, which had been named after him by his father.

In 1271-1272 he took part in the Polish succession war on the side of Bolesław the Chaste together with his brother Mstislav, Prince of Lutsk, and later joined his cousin Volodymyr Vasylkovych in a campaign against the Jotvingians, which ended with the latter suing for peace.

However, he refused to personally join the Lithuanian troops and prevented his sone Yuri from taking part in the campaign, fearing revenge for the murder of Vaišvilkas.

[5] In 1289 he personally visited his ally Wenceslaus in Opava and returned to Lviv with lavish gifts, as well as rich booty captured from the Poles.

Leo is seen as an important figure in Rus' history due to his development of Lviv, the capital of Galicia, of which he was long reputed to be the founder (although historical chronicles attribute its foundation to his father, King Daniel).