Despite being of patrician descent, he supported the plebeian wish for a code of laws, and while in office shared power with their representatives. Thus a decemviri (council of ten) was established to ratify new laws, a process where the decemvirs had total authority over Rome, even suspending the current powers of the tribunes and other administrative officers. Although Appius served on full year term to ratify Rome's new laws off the Greek model, his council convinced the public to have them serve another annual term as decemvirs in order to ratify two more engraved tables to the laws (which would become the Twelve Tables of Rome).
When it came time to re-appoint a new council of ten lawmakers, the patricians became suspicious that Appius growing popularity would gain for him enough favor to be re-appointed. So they pressed upon Appius to propose who should serve in the next decemviri. To everyone's surprise he proposed himself to sit on the next council, whereas everyone thought he would decide to act modestly by declining the offer and adding his name to the list. The people became even more suspicious once Appius increased the traditional size of the guarding body of lictors from the mere twelve men to one hundred and twenty.
When the end of their second year of power came to an end, the decemvirs had the Twelve Tables completed, but not yet published for public view, and so used this as an excuse to retain their powers. Everyone became upset with the decemvirs, the patricians forced into violent factions and the plebeians fearful of their liberties being taken.
However, when the Sabines and the Volsci made a sudden assault on Rome, the decemvirs realized the weakness of their position without a functioning Roman Senate in office to handle the threat. So they called the Senate back into session, which was an opportune moment for senators such as Valerius and Horatius to point out the arrogance of the decemvirs. A civil war broke out between the decemvirs and the senators, and in the end the decemvirs lost, while the consulship and tribunate were reestablished.
Appius' decemviral code survived the overthrow of the decemvirs ca 449 BC. He was claimed to have been murdered or committed suicide as a consequence of his lust for Verginia, but the historical facts are scanty and dubious.