In 227 BC he lost the elections against Aratus of Sicyon, but was chosen as hipparch, in this position he fell at the gates of his city during a cavalry charge against the Spartan king Cleomenes III.
Almost nothing is known of the steps by which he rose to power, but the sources represent him as a man of an ambitious yet generous character, who was misled by false rhetorical arguments to believe that a monarchical government was the best for his fellow-citizens.
His desire for fame and his wish to distinguish the year of his command through some brilliant exploit led him to plan an expedition against Sparta, which was, however, opposed by Aratus, who is said to have already begun to be jealous of Lydiadas' favour and reputation.
But though Lydiadas was unable to shake Aratus' long-established standing, he maintained his ground, not withstanding the insidious attacks of his rival, and the suspicion that naturally attached to one who had formerly borne the name of tyrant.
His body was left on the field, but Cleomenes had the generosity to honour a fallen foe, and sent it back to Megalopolis, adorned with the insignia of royal dignity.