He was the son of the oracle Amphiaraus and Erifili. He was one of the Epigoni, one of the children of the Seven Generals, who had also campaigned against Thebes.
In this campaign he took part to avenge the death of his father. He excelled in the battlefield and killed the King of Thebes, Laomedon, son of Polyneikes.
When he returned from this campaign, he killed his mother to punish her for her double treason, betrayal against him and against his father. Polyneikes son of Oedipus wanted to campaign against Thebes. His purpose was to claim the throne from his brother Eteocles. So he asked for the help of the Seven Generals, among them Amphiaraos. He initially refused to take part, because, as an oracle , he knew that from all the leaders only Adrastos would return alive. But his wife, Erifili, persuaded him, and here’s why: Polyneikes had promised that if she could persuade her husband to take part in the campaign, he would give her the famous necklace of Harmony. So it happened. Amphiaraus was persuaded, but ordered his sons to kill their mother after the unfortunate end of the war and to campaign against Thebes. But in this case Erifili also betrayed her own. This time, she received the veil of Harmony from the son of Polyneikes Thersandros to persuade her sons to take part in the Epigonian campaign. After the fall of Thebes, Alkmaion killed her, when he learned of the bribe. It was natural for Erinyes to persecute him for this murder. That is why he had to resort to the king of Arkadia, Phigeas. He helped him to purify himself from the murder of his mother and gave him his daughter Alphesivoea or Arsinoe for wife. Erinyes , however, continued to persecute him.
He then asked for a sign from the oracle. He was advised to go to a country that had not seen the sunlight when he killed his mother. Thus it was found in the estuary of Acheloos River, where the land around was formed by the floods of the river after his crime. There, he was purified for the second time and Acheloos gave him his daughter Kalliroe for wife. She begged him to bring her the veil and necklace of Harmony, taken by his mother Erifili, as a reward for her double betrayal. Alkmaion, however, had given them to Alphesivoea, the daughter of Fygeas. On the pretext that he wanted to dedicate them to Apollo, he took them back. But Fygea's sons killed him in ambush. However soon enough they also found death from the sons of Alkmaion, Acarnanas, and Amphoteros, who suddenly became men.
