He was the fifth child and the second son of Archduke Charles Stephen of Austria and Archduchess Maria Theresia, Princess of Tuscany.

Archduke Leo Karl was his father’s answer to the Eastern European question, and became the would-be Regent of the Habsburgs' zone of influence in the Balkan region.

In 1913, Leo and his younger brother, Wilhelm, enrolled at the Theresian Military Academy in Wiener-Neustadt.

He lived on a portion of the Żywiec family estate that he and his brother, Albrecht, inherited from their father.

He was buried in the local cemetery in Bestwina, a countryside plot belonging to his family.