Aristides was an Athenian statesman, nicknamed "the Just". Plato called him the only man in Athens worth admiring. His family was of moderate fortune. Of his early life we are only told that he became a follower of the statesman Cleisthenes and sided with the aristocratic party in Athenian politics. He first came to notice as strategos in command of his native tribe Antiochis at the Battle of Marathon, and it was no doubt in consequence of the distinction which he then achieved that he was elected archon for the ensuing year (489–488). In pursuance of a conservative policy which aimed at maintaining Athens as a land power, he was one of the chief opponents of the naval policy of Themistocles.
The conflict between the two leaders ended in the ostracism of Aristides, at a date variously given between 485 and 482. It is said that, on this occasion, an illiterate voter, who did not know him, came up to him, and giving him his voting sherd, desired him to write upon it the name of Aristides. The latter asked if Aristides had wronged him. "No," was the reply, "and I do not even know him, but I am tired of hearing him everywhere called, 'The Just'." After hearing this Aristides wrote his own name on the sherd. He was then exiled for a period of five years. Early in 480 Aristides profited by the decree recalling exiles to help in the defence of Athens against Persian invaders, and was elected strategos for the year 480–479. In the Battle of Salamis he gave loyal support to Themistocles, and crowned the victory by landing Athenian infantry on the island of Psyttaleia and annihilating the Persian garrison stationed there.
In 479 he was re-elected strategos, and given special powers as commander of the Athenian forces at the Battle of Plataea; he is also said to have suppressed a conspiracy among some oligarchic malcontents in the army. He so won the confidence of the Ionian allies that, after revolting from the Spartan admiral Pausanias, they gave him the chief command and left him with absolute discretion in fixing the contributions of the newly formed confederacy, the Delian League. His assessment was universally accepted as equitable, and continued as the basis of taxation for the greater part of the league’s duration.
He continued to hold a predominant position in Athens. At first he seems to have remained on good terms with Themistocles, whom he is said to have helped in outwitting the Spartans over the rebuilding of the walls of Athens. He is said by some authorities to have died at Athens, by others on a journey to the Black Sea. The date of his death is given by Nepos as 468; at any rate he lived to witness the ostracism of Themistocles, towards whom he always displayed generosity, but he died before the rise of Pericles. His estate seems to have suffered severely from the Persian invasions, for apparently he did not leave enough money to defray the expenses of his burial, and it is known that his descendants even in the 4th century received state pensions.