Under Nikephoros I, Leo had a mixed career: he was named commander of the foederati, but then exiled either for illegal personal enrichment or for his support of the rebel Arsaber. Michael I (Nikephoros's son–in–law) recalled Leo from exile in 811 and named him strategos of the Anatolikon. His troops were reportedly the first to flee from the disastrous battle of Versinikia in June 813, and three weeks later these same troops proclaimed Leo emperor. Michael I was deposed and his sons were castrated. Granted a reprieve by the deaths of Byzantium’s two great enemies, Khan Krum and Caliph Harun al-Rashid, Leo was able to strengthen the defenses of Thrace and extend the capital’s walls at Blachernai. Following the disastrous records of Eirene and Nikephoros I, Leo reinstated Iconoclasm at the Local Council of 815 in Constantinople. In his approach to Iconoclasm, Leo consciously modelled himself on Leo III, removing the icon of Christ from the Chalke gate, and even renaming his son Constantine. Leo appointed the future emperor Michael II the Amorian and the future rebel Thomas the Slav to high military commands, decisions that would have serious repercussions for Leo himself and for Byzantium. Arrested on charges of treason, Michael the Amorian was sentenced to be burned alive while tied to an ape. Before the sentence could be carried out his co-conspirators, dressed as priests, murdered Leo in church on Christmas Day 820.
The return of Iconoclasm marks as well the return of aniconic seals with a cross potent on the obverse and an inscription on the reverse. Leo’s son Smbat was crowned as Constantine and associated with him as emperor. Their seals thus mark the culmination of a century-long procession of inscriptions reading “Leo and Constantine, faithful basileis of the Romans.”