Son of Eudamidas II., of the Eurypontid family, commonly called Agis IV. He succeeded his father probably in 245 BC, in his twentieth year. At this time the state had been brought to the brink of ruin by the growth of avarice and luxury; there was a glaring inequality in the distribution of land and wealth, and the number of full citizens had sunk to 700, of whom about 100 practically monopolized the land.

Though reared in the height of luxury he at once determined to restore the traditional institutions of Lycurgus, with the aid of Lysander, a descendant of the victor of Aegospotami, and Mandrocleidas , a man of noted prudence and courage; even his mother, the wealthy Agesistrata , threw herself heartily into the cause. A powerful but not disinterested ally was found in the king's uncle, Agesilaus, who hoped to rid himself of his debts without losing his vast estates.

Lysander as ephor proposed on behalf of Agis that all debts sbould be cancelled and that Laconia should be divided into 19,500 lots, of which 4500 should be given to the Spartans, whose number was to be recruited from the best of the perioeci and other foreigners, and the remaining 15,000 to perioeci who could bear arms. The Agiad king Leonidas having prevailed on the council to reject this measure, though by a majority of only one, was deposed in favour of his son-in-law Cleombrotus, who assisted Agis in bearing down opposition by the threat of force.

The abolition of debts was carried into effect, but the land distribution was put off by Agesilaus on various pretexts. At this point Aratus appealed to Sparta to help the Achaeans in repelling an expected Aetolian attack, and Agis was sent to the Isthmus at the head of an army. In his absence the open violence and extortion of Agesilaus, combined with the popular disappointment at the failure of the agrarian scheme, brought about the restoration of Leonidas and the deposition of Cleombrotus, who took refuge at the temple of Apollo at Taenarum and escaped death only at the entreaty of his wife, Leonidas's daughter Chilonis.

On his return Agis fled to the temple of Athena Chalcioecus at Sparta, but soon afterwards he was treacherously induced to leave his asylum and, after a mockery of a trial, was strangled in prison, his mother and grandmother sharing the same fate (241). Though too weak and good-natured to cope with the problem which confronted him, Agis was characterized by a sincerity of purpose and a blend of youthful modesty with royal dignity, which render him perhaps the most attractive figure in the whole of Spartan history.