Avitus, the future Western Roman Emperor, was born in Clermont, to a family of the Galllo-Roman nobility.

His father was possibly Flavius Julius Agricola, consul in 421.

Avitus had followed a course of study typical for a young man of his rank, including law.

Before 421, he had been sent to the powerful patricius Flavius Constantius (briefly Emperor in 421), to ask for a tax reduction for his own country.

This embassy was successful.

A relative of his, Theodorus, had been hostage at the court of the King of Visigoths, Theodoric I: in 425/426 Avitus had gone and met him, thus meeting the King, who had let Avitus enter his own court.

Avitus had then started a military career, serving under the magister militum Flavius Aetius in his campaign against the Juthungi and the Norics (430–431) and also against the Burgundians (436).

Because the Romans had had to fight against the Franks, who had plundered Cologne and Trier in 435, and because of other events, Theodoric I, King of the Visigoths, sees the chance to conquer Narbo Martius (in 436) to obtain access to the Mediterranean Sea and the roads to the Pyrenees.