Nothing is known of his early life, but judging from his Latin name "Petasius" (little felt sun-hat) he was a native of Italy. He claimed imperial power around 729 when large parts of Italy and rest of the empire rebelled against Iconoclastic policies of EmperorLeo III, who had been excommunicated by Pope Gregory II. He may have been chosen by local Italian assemblies with the intention eventually taking power in Constantinople, but failed uprisings in Greece seem to have disheartened courage of Italians with the issue. His power seems to have been centered around the area of Rome, but nothing else is known of his short stay in power. Tiberius Petasius' power came to an end sometime in 730 when he was defeated by Exarch of RavennaEutychius with support of Pope Gregory II and killed in Monterano, with his head sent to Leo III as a gift.