Made magister militum (or Master of Soldiers) by Emperor Petronius Maximus, Avitus was sent on a diplomatic mission to his old student, Theodoric II King of the Visigoths, and was at Theodoric's court in Toulouse when Gaiseric invaded Rome, bringing Petronius Maximus's rule to a sudden end. Theodoric seized the opportunity and urged Avitus to assume the imperial throne, and with the acclamation of a gathering of Gallo-Roman senators, allowed himself to be persuaded. On July 9, 455, he was proclaimed emperor by the soldiers, and reached Rome that September.
The Apenninian populace never fully accepted his rule, so when his campaign against the Vandals failed in 456, and they pressed their blockade against Rome, his position became tenuous. Famine in Rome forced him to disband his Gothic bodyguard. But they needed to be paid, and he did not improve his standing with the Roman citizenry when he melted down a number of bronze statues to pay their outstanding wages. Ricimer and Majorian exploited this discontent by starting a general revolt.
Avitus fled to safety in Arles. A plea for help to Theodoric went unanswered, as the Gothic king was away in Spain campaigning against the Suevians. Avitus raised the best force he could and returned to Italy. He was defeated near Placentia and captured. His life was spared, and was allowed to become bishop of Placentia on October 17 (or October 18), 456; however, he still feared for his life and attempted to escape to safety in Gaul. According to Gregory of Tours, he died on the way there. Other sources have him murdered, either being strangled personally by Ricimer or trapped in his house and starved to death.
His son was the magister militum Ecdicius Avitus and his grandson was the poet Alcimus Ecdicius Avitus. He was also the father of Agricola (440 – after 507), v. inl., a Priest, whose daughter also named Papianilla (490 – 530) married her relative (?) Parthenius (485 – 548), a Patron in 542 and perhaps a great-grandson of Felix Ennodius.