Amlaith was the eldest son of Eärendur, the tenth King of Arnor.
He was destined to become King of Arnor after his father's death, but there were constant quarrels between Eärendur's sons.
A civil war erupted when Eärendur finally died. Amlaith, however, failed to overcome his two brothers and founded the kingdom of Arthedain. (His brothers founded the kingdoms of Cardolan and Rhudaur).
His reign in Arthedain was largely a peaceful one.
He was succeeded by his son Beleg.