As plebeian tribune, Clodius enacted laws designed to strengthen his support among the urban plebs and neutralize Cicero’s backers. Hence, when a Clodian law criminalizing the execution of citizens without a trial was put to a vote, Cicero preemptively departed into exile in mid-March 58. Another Clodian law was then enacted, formalizing Cicero’s banishment and requiring him to remain 500 miles from Rome. Cicero found refuge with Cn. Plancius, a quaestor based in Thessalonica. In 57, however, the new magistrates, led by the consul Lentulus Spinther, pushed for Cicero’s recall. After the plebeian tribunes Milo and P. Sestius organized their own gangs to counter Clodius’, the latter lost control of the streets, and Cicero’s recall took shape. He arrived back in Italy in August and entered Rome on September 4, delivering speeches in the senate and before the people that expressed thanks and vowed a continuation of his previous policies.

Disappointed by this second defeat, Catiline formed a conspiracy to overthrow the government and install himself in power. He acted in league with C. Manlius, who had gathered a band of Sullan veterans and other malcontents in Faesulae (in Etruria). Cicero’s warnings to the senate were at first disbelieved. But when the conspirators’ rising in Etruria was independently confirmed, he obtained the senatus consultum ultimum authorizing him as consul to act in the defense of the state. The waiting continued until, on the night of 6–7 November, assassins appointed by Catiline appeared at Cicero’s door. He had, however, been forewarned and denied them entry. That event spurred Cicero to denounce Catiline in the senate (Catilinarian 1), leading Catiline to depart Rome. Though further conspirators remained in the City, Cicero was able to obtain evidence against them and a decree of the senate calling for their execution, which he supervised.

Cicero continues his philosophical writing with a cosmological work, On the Universe, which he seems to have abandoned in favor of the dialogue On the Nature of the Gods, which set out and refuted the theologies of the Epicureans and Stoics. This was supplemented by On Divination, a dialogue between Cicero and his brother, Quintus. He also wrote the short dialogue On Old Age to honor his friend Atticus on his sixty-fifth birthday. His last quasi-forensic speech was a defense before Caesar of the Galatian tetrarch Deiotarus; the matter was still pending at Caesar’s death. He continued to attend meetings of the senate but was privately critical of the hollowing out of republican institutions under Caesar’s dictatorship. Caesar’s assassination on the Ides of March raised brief hopes of a return to republican patterns of government, but Mark Antony, who had been Caesar’s co-consul, was quickly able to reassert control.