A son of Oicles and Hypermnestra, the daughter of Thestius. (Hom. Od. xv. 244; Apollod. i. 8. § 2; Hygin. Fab. 73; Paus. ii. 21. § 2.) On his father's side he was descended from the famous seer Melampus. (Paus. vi. 17. § 4.) Some traditions represented him as a son of Apollo by Hypermnestra, which, however, is merely a poetical expression to describe him as a seer and prophet. (Hygin. Fab. 70.) Amphiaraus is renowned in ancient story as a brave hero : he is mentioned among the hunters of the Calydonian boar, which he is said to have deprived of one eye, and also as one of the Argonauts. (Apollod. i. 8. § 2, 9. § 16.) For a time he reigned at Argos in common with Adrastus ; but, in a feud which broke out between them, Adrastus took to flight. Afterwards, however, he became reconciled with Amphiaraus, and gave him his sister Eriphyle in marriage [see ADRASTUS], by whom Amphiaraus became the father of Alcmaeon, Amphilochus, Eurydice, and Demonassa. On marrying Eriphyle, Amphiaraus had sworn, that he would abide by the decision of Eriphyle on any point in which he should differ in opinion from Adrastus. When, therefore, the latter called upon him to join the expedition of the Seven against Thebes, Amphiaraus, although he foresaw its unfortunate issue and at first refused to take any part in it, was nevertheless persuaded by his wife to join his friends, for Eriphyle had been enticed to induce her husband by the necklace of Harmonia which Polyneices had given her. Amphiaraus on leaving Argos enjoined his sons to avenge his death on their heartless mother. (Apollod. iii. 6. § 2; Hygin. Fab. 73; Diod. iv. 65; Hom Od. xv. 247, &c.) On their way to Thebes the heroes instituted the Nemean games, and Amphiaraus won the victory in the chariot-race and in throwing the discus. (Apollod. iii. 6. § 4.) During the war against Thebes, Amphiaraus fought bravely (Pind. Ol. vi. 26, &c.), but still he could not suppress his anger at the whole undertaking, and when Tydeus, whom he regarded as the originator of the expedition, was severely wounded by Melanippus, and Athena was hastening to render him immortal, Amphiaraus cut off the head of Melanippus, who had in the mean time been slain, and gave Tydeus his brains to drink, and Athena, struck with horror at the sight, withdrew. (Apollod. iii. 6. § 8.) When Adrastus and Amphiaraus were the only heroes who survived, the latter was pursued by Periclymenus, and fled towards the river Ismenius. Here the earth opened before he was overtaken by his enemy, and swallowed up Amphiaraus together with his chariot, but Zeus made him immortal. (Pind. Nem. ix. 57, Ol. vi. 21, &c.; Plut. Parall. 6; Cic. de Divin. i. 40.) Henceforth Amphiaraus was worshipped as a hero, first at Oropus and afterwards in all Greece. (Paus. i. 34. § 2; Liv. xlv. 27.) He had a sanctuary at Argos (Paus. ii. 23. § 2), a statue at Athens (i. 8. § 3), and a heroum at Sparta. (Müller, Orchom. pp. 146, 486.) The departure of Amphiaraus from his home when he went to Thebes, was represented on the chest of Cypselus. (Paus. v. 17. § 4.) Respecting some extant works of art, of which Amphiaraus is the subject, see Grüneisen, Die alt griechische Bronze des Tux'schen Kabinets in Tübingen, Stuttg. and Tübing. 1835.
The prophetic power, which Amphiaraus was believed to possess, was accounted for by his descent from Melampus or Apollo, though there was also a local tradition at Phlius, according to which he had acquired them in a night which he spent in the prophetic house (oikos mantikos) of Phlius. (Paus. ii. 13. § 6; comp. i. 34. § 3.) He was, like all seers, a favourite of Zeus and Apollo. (Hom. Od. xv. 245.) It should be remarked here, that Virgil (Aen. vii. 671) mentions three Greek heroes as contemporaries of Aeneas, viz. Tiburtus, Catillus, and Coras, the first of whom was believed to be the founder of Tibur, and is described by Pliny (H. N. xvi. 87) as a son of Amphiaraus.