Nothing is known of Leo's early life except that he was born in or near Attaleia, the capital of the maritime Cibyrrhaeot Theme, and was captured in an Arab raid and brought to Tripoli.

[1][2] In Arabic sources he is called Lāwī Abū'l-Ḥārith and given the sobriquet ghulām Zurāfa, "servant/page of Zurafa", probably reflecting the name of his first Muslim master.

[3][4] The details of Leo's early career in the Muslim fleets are unknown, but he seems to have risen quickly: the historian Mas'udi, who met him in person, regarded him as one of the best navigators of his time.

[2] In the summer of 904, Leo was at the head of a major Abbasid naval expedition of 54 vessels from the Syrian and Egyptian fleets, whose initial target reportedly was Constantinople itself.

The Arab fleet penetrated the Dardanelles and sacked Abydos, as the Byzantine navy under the droungarios Eustathios Argyros was reluctant to confront them.