[2] Agis was the son of Eudamidas II (r. c.275–c.245) and grandson of Archidamus IV (r. c.300–c.275), who belonged to the Eurypontid dynasty, one of the two royal families of Sparta (the other being the Agiads).

The reign of Agis marks a re-emergence of the Eurypontids, who had disappeared from the records since the defeat of Archidamus IV against Demetrios Poliorketes in 294.

Another part of his plan was to give landed estates to the Perioikoi capable of bearing the arms, and to the Metic women, "who had a beautiful appearance and were in prime of their life".

He succeeded, however, in gaining over three very influential persons: his uncle Agesilaus (a man of large property, but who, being deeply involved in debt, hoped to profit by the innovations of Agis), Lysander (a descendant of the victor of Aegospotami) and Mandrocleides.

Lysander, therefore, convened the assembly of the people, to whom Agis submitted his measure, and offered to make the first sacrifice, by giving up his own lands and money, telling them that his mother, Agesistrate, and grandmother, who were both possessed of great wealth, with all his relations and friends, would follow his example.

Soon afterwards, however, Lysander's term of office expired, and the ephors of the following year were opposed to Agis, and looked to restore Leonidas.

The cautious movements of the Achaean leader, Aratus of Sicyon, gave Agis no opportunity to distinguish himself in battle, but he gained great credit by the excellent discipline he preserved among his troops.

During his absence Agesilaus so angered the poorer classes by the continued postponement of the division of the lands, that they made no opposition when the enemies of Agis openly brought back Leonidas II and set him on the throne.

He was accused of seeking tyranny, and quickly executed by strangulation, the ephors fearing a rescue, as a great crowd of people had assembled around the prison gates.

[12] His widow Agiatis was forcibly married by Leonidas to his son Cleomenes III, but nevertheless the two developed for each other a mutual affection and esteem.

[13][14] Considered by many writers too weak and good-natured to cope with the problems 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.