An ancient Irpinian centre, it submitted to Rome in 209 AD., becoming a Roman colony and busy agricultural and trading centre. Severely damaged during the war between Goths and Byzantines, it was rebuilt by the Lombards after the fall of the Roman Empire, on its present site only a few kilometres from the original settlement, and grew in importance to become the capital of a County.

Conquered by the Normans at the beginning of the 12th century, it shared the vicissitudes of the Kingdom of Naples, though the fief of various overlords; those who held it for the longest periods of time were the Dell'Aquilas (12th century), the Del Balzos (12th-14th centuries) and the Caracciolo family, whose rule lasted from 1581 to 1806. Avellino became part of Italy in 1860.