Ephialtes was leader of the democratic opposition in Athens (462-461). The most powerful political leader at the time was Cimon, son of Miltiades. He was an aristocrat and not willing to privide Athens more democratic rights. By ostracism, Cimon was sent away which gave Ephialtes the opportunity to restrict the Areopagus's power. The Areopagus (or Areopagos) was the last of the aristocratic bastions in Athens.

Ephialtes turned the right to supervise the archons (the political leaders) over to the people's Council of 500 (boulè). This restricted the archons' freedom of action hugely. The council also checked upon their antecedents and could dismiss them immediately at the start of each prytany, the bouleutai's term of office. Civilians could now ask the council to investigate a political leader.

The people's lawcourt (hèliaia) received all the Areopagus' legislative powers but the murder cases. Thanks to Ephialtes this democratic court rose in importance. Yearly 6000 volunteers were drawn in a lottery, to form a huge reservoir of judges who took place in a special jury, called dikastèrion. The number of jury members depended on the importance of the case, but was enormous to our standards (to prevent bribes). The court that sentenced Socrates in 399 consisted of 501 jury members.

Ephialtes was killed in 461.