Of the youth of Agesilaus we have little detail, beyond the mention of his intimacy with Lysander. We do know that he was not expected to succeed to the throne after his brother, king Agis II, since the latter had a son, named Leotychidas, and so Agesilaus was trained in the traditional curriculum of Sparta, the agoge. But Leotychidas was ultimately set aside as illegitimate, contemporary rumors representing him as the son of Alcibiades, and Agesilaus became king around 401 BC, at the age of about forty. In addition to questions of his nephew's paternity, Agesilaus' succession was largely due to the intervention of his former eispnelas (pederastic lover), the Spartan general Lysander, who hoped to find in him a willing tool for the furtherance of his political designs.
It was said that in 394 BC, while encamped on the plain of Thebe, he was planning a campaign in the interior, or even an attack on Artaxerxes II himself, when he was recalled to Greece owing to the war between Sparta and the combined forces of Athens, Thebes, Corinth, Argos and several minor states. A rapid march through Thrace and Macedonia brought him to Thessaly, where he repulsed the Thessalian cavalry who tried to impede him. Reinforced by Phocian and Orchomenian troops and a Spartan army, he met the confederate forces at Chaeronea in Boeotia, and in a hotly contested battle was technically victorious, but the success was a barren one and he had to retire by way of Delphi to the Peloponnese. Shortly before this battle the Spartan navy, of which he had received the supreme command, was totally defeated off Cnidus by a powerful Persian fleet under Conon and Pharnabazus. In 393 BC, Agesilaus engaged in a ravaging invasion of Argolis. In 392 BC he took a prominent part in the Corinthian War, making several successful expeditions into Corinthian territory and capturing Lechaeum and Piraeus. The loss, however, of a mora, destroyed by Iphicrates, neutralized these successes, and Agesilaus returned to Sparta. In 389 BC he conducted a campaign in Acarnania, but two years later the Peace of Antalcidas, warmly supported by Agesilaus, put an end to hostilities. In this interval, we find him declining the command in Sparta's aggression on Mantineia, but heading, from motives of private friendship, that on Phlius, and openly justifying Phoebidas' seizure of Cadmea.
In 370 BC we find Agesilaus engaged in an embassy to Mantineia, and reassuring the Spartans by an invasion of Arcadia. His prudence and heroism preserved an un-walled Sparta against the revolts and conspiracies of helots, perioeci and even Spartans, and against her enemies, four different armies led by Epaminondas, that penetrated Laconia that same year, and again in 362 BC when they all but succeeded in seizing the city by a rapid and unexpected march. The Battle of Mantinea, in which Agesilaus took no part, was followed by a general peace: Sparta, however, stood aloof, hoping even yet to recover her supremacy. According to an obscure passage of Xenophon, Agesilaus, in order to gain money for prosecuting the war, supported the satrap Ariobarzanes II in his revolt against Artaxerxes II in 364 BC, and in 361 BC he went to Egypt at the head of a mercenary force to aid the king Nectanebo I and his regent Teos against Persia. He soon transferred his services to Teos's cousin and rival Nectanebo II, who, in return for his help, gave him a sum of over 200 talents. On his way home Agesilaus died in Cyrenaica, around the age of 84, after a reign of some 41 years. His body was embalmed in wax, and buried at Sparta.
As a statesman he won himself both enthusiastic adherents and bitter enemies. Referring to the above sketch of Spartan history, we find Agesilaus shining most in its first and last period, as commencing and surrendering a glorious career in Asia, and as, in extreme age, maintaining his prostrate country. Other writers acknowledge his extremely high popularity at home, but suppose his occasionally rigid and even irrational political loyalties and convictions contributed greatly to Spartan decline, notably his unremitting hatred of Thebes, which led to Sparta's humiliation at the Battle of Leuctra and thus the end of Spartan hegemony.
We have reduced most of Asia, driven back the barbarians, made arms abundant in Ionia. But since you bid me, according to the decree, come home, I shall follow my letter, may perhaps be even before it. For my command is not mine, but my country's and her allies'. And a commander then commands truly according to right when he sees his own commander in the laws and ephors, or others holding office in the state.
And when asked whether he wanted a memorial erected in his honor:
If I have done any noble action, that is a sufficient memorial; if I have done nothing noble, all the statues in the world will not preserve my memory.
He lived in the most frugal style alike at home and in the field, and though his campaigns were undertaken largely to secure booty, he was content to enrich the state and his friends and to return as poor as he had set forth.