Valerius had expected to become one of the consuls and retired from public life in a huff (509). There was speculation that he and others might side with the Tarquins if they ever tried to return by force, and so the whole senate, led by Valerius took an oath never to surrender to the Tarquins.
This oath was not enough to quiet the people's fears, and Lucius Tarquinius Collatinus, as part of the Tarquin family, was also forced to go into exile (although Brutus was more nearly related by blood it was through his mother, and so he was not counted as part of the Tarquin family). Valerius was elected consul to replace him.
Under cover of negotiations for the return of their property, the Tarquins made contact with some young nobles who were unhappy with the new order of things and a conspiracy was launched. The conspirators swore on the entrails of a human sacrifice not to reveal the details of the plot, but they were overheard by a slave, Vindicius, who informed Valerius. The conspirators were arrested, incriminating letters were found, the plot was foiled. Valerius produced the slave and after a short trial the conspirators were sentenced to death. One of the conspirators was Brutus' own son, but Brutus watched unflinchingly as the young man was put to death.
The Aquilii family, some of whose members were among the conspirators and who were the owners of Vindicius, demanded that he be surrendered to them. Valerius refused, and instead freed Vindicius and made him a Roman citizen, thus setting a precedent for other freed slaves to become citizens.
The conspiracy having failed, the Tarquins tried to return by force, and allied themselves with the Etruscan towns of Veii and Tarquinii, their ancestral town, to attack Rome. Valerius and Brutus led out the Roman troops into battle. Both sides lost many men Brutus was among the slain but during the night a mysterious voice was heard coming from a nearby wood, saying that the Etruscans had lost one more man than the Romans, and the Romans had therefore won.
Valerius returned to Rome to celebrate his triumph and hold Brutus' funeral. Valerius did not immediately hold elections for a consul to succeed Brutus and was building a magnificent new house for himself. Rumours spread that he wanted to make himself king. When he heard of the rumours, Valerius demolished the house, and stayed with friends until he had had a more modest house built. He also started the custom of the consuls lowering the fasces (the rods carried by their attendants) when they came into assemblies as a sign that they derived their power from the people.
Before holding elections for a colleague to be elected, Valerius enacted some important legislation: the right of appeal to the people from magistrates' judgements; capital punishment for assuming a magistracy not granted by the people; the abolition of taxes on citizens; a fine for disobeying the consuls; loss of civil rights for plotting the return of the monarchy; and death without trial for plotting to make oneself king. He also instituted the public treasury in the temple of Saturn and the election of quaestors to administer it. Because these measures were considered to be in the interests of the common people rather than the patricians, Valerius was granted the new name of Publicola (sometimes spelt Poplicola), meaning People-Minder. The elections for a consul to replace Brutus then went ahead and Spurius Lucretius was elected. However, he died a few days later and another election had to be held. Marcus Horatius was then elected for the remainder of the year.