He was born as the son of David I, a member of the genus (clan) Aba, who was mentioned as ispán (comes) in contemporary sources and ancestor of the Berthóty family.

In 1280, Aba became the head of Hermannstadt (today Sibiu in Romania), i.e., the royal officer appointed to administer the Transylvanian Saxons.

Charles laid siege to Buda, the capital of the kingdom, in September 1302, but Ivan Kőszegi relieved the town.

In 1304, Scepusian Saxons and the citizens of Kassa supported by Wenceslaus unsuccessfully besieged Amadeus' centre, Gönc.

In 1304 and 1305, he gave military assistance to Duke Władysław of Cuiavia against King Wenceslaus II who had occupied Lesser Poland.

This case proves that Amadeus followed an independent foreign policy, similarly to the other oligarchs of the realm.

Amadeus Aba was present at the Assembly of Rákos (10 October 1307) where the participants confirmed Charles' claim for the throne.

Two of his sons, Amadeus II and Dominic were captured and held hostage alongside other 45 family members and vassals.

Amadeus arbitrarily imposed duties and built castles and appointed castellans among his familiars without the permission of the king.

According to a diploma issued in 1302, his troops seized the possessions of a local noble in Abaúj County and the owner himself was imprisoned and threatened with death to persuade him to pass on the family's deed of gift.

Amadeus Aba exercised sovereign rights in his domain but remained loyal to the kings (he rebelled against the central power only once in 1288, when the unpopular Ladislaus IV lost all domestic and foreign support), thus Zsoldos refers to him as a "loyal oligarch", alongside Stephen Ákos.

Nonetheless, his sons could not maintain his power, and after their defeat at the Battle of Rozgony (today Rozhanovce in Slovakia) his dominion disintegrated.

Taking advantage of their downfall, Peter, son of Petenye built up a dominant power in Zemplén County, while some of Amadeus' former castles and possessions were obtained by members of the Drugeth family in the 1320s–1340s.