In 409, with the decline of the Roman Empire, the Iberian Peninsula was occupied by Germanic tribes that the Romans referred to as barbarians. In 411, with a federation contract with Emperor Honorius, many of these people settled in Hispania. An important group was made up of the Suebi and Vandals in Gallaecia, who founded a Suebi Kingdom with its capital in Braga. They came to dominate Aeminium (Coimbra) as well, and there were Visigoths to the south. The Suebi and the Visigoths were the Germanic tribes who had the most lasting presence in the territories corresponding to modern Portugal. As elsewhere in Western Europe, there was a sharp decline in urban life during the Dark Ages.

Roman institutions disappeared in the wake of the Germanic invasions with the exception of ecclesiastical organizations, which were fostered by the Suebi in the fifth century and adopted by the Visigoths afterwards. Although the Suebi and Visigoths were initially followers of Arianism and Priscillianism, they adopted Catholicism from the local inhabitants. St. Martin of Braga was a particularly influential evangelist at this time.

In 429, the Visigoths moved south to expel the Alans and Vandals and founded a kingdom with its capital in Toledo. From 470, conflict between the Suebi and Visigoths increased. In 585, the Visigothic King Liuvigild conquered Braga and annexed Gallaecia. From that time, the Iberian Peninsula was unified under a Visigothic Kingdom.