Upon his return to Rome, he attempted to stand for the consulship but was rebuffed; he then was beset with legal challenges over alleged corruption in Africa and his actions during Sulla's proscriptions (83–82 BC).

Defeated in the consular comitia, he concocted a plot to take the consulship by force, bringing together poor rural plebs, Sullan veterans, and other senators whose political careers had stalled.

Crassus revealed the coup attempt – which involved armed uprisings in Etruria – to Cicero, one of the consuls, in October 63 BC, but it took until November before evidence of Catiline's participation emerged.

Sallust, in his monograph on the conspiracy, Bellum Catilinae, painted Catiline as a symbol of the Roman Republic's moral decline, as much of a victim as a perpetrator, as his characterization of "a ravaged mind" (vastus animus) indicates.

[1][page needed] Catiline was a member of an ancient patrician family, the gens Sergia, who claimed descent from Sergestus, a Trojan companion of Aeneas.

[17] Regardless, Catiline did engage in profiteering from the Sullan proscriptions, likely purchasing estates for fractions of their true value, and by the end of Sulla's dictatorship, he had become a rich man.

[18] In 73 BC, he may have been prosecuted for adultery – apud pontifices (before a panel of pontiffs as judges) – with a Vestal Virgin named Fabia, a half-sister of Cicero's wife Terentia.

Cicero's allegations "cannot be taken at face value and reveal more about typical themes and slanders found in Roman invective than they do about Catiline's domestic history".

[49] Cicero spoke out against it, warning of tyrannical land commissioners and painting the project as selling out the people to the beneficiaries of the Sullan proscriptions.

Cicero supported Sulpicius' bid as a friend and fellow lawyer, which directly harmed Catiline's chances, since both men were patricians and therefore were legally barred from both holding the consulship.

[55] Just before the elections, Cicero alleges Catiline engaged in demagoguery and attempted to build up his bona fides with the poor and dispossessed men of Rome and Italy, including himself among their number,[56] advocating the wholesale abolition of all existing debts (tabulae novae).

[57] At the electoral comitia, Cicero presided, surrounded by a bodyguard and wearing an ostentatious cuirass, to signal his belief that Catiline posed a threat to his person and public safety.

[62] On 18 or 19 October, Crassus and two other senators visited Cicero's house on the Oppian Hill (near the ruins of the Colosseum) and delivered to the consuls anonymous letters, warning that Catiline was planning a massacre of leading politicians, and advising them to leave the city.

[58] A few days later, on 21 or 22 October, an ex-praetor reported news that an ex-Sullan centurion – Gaius Manlius – who had supported Catiline's bid for the consulship had raised an army in Etruria.

[63] The senate acted immediately, usually dated to the 21st, to pass a senatus consultum ultimum directing the consuls to take whatever actions they believed necessary for state security.

[64] Catiline's indebtedness – if he was in fact indebted, there is little evidence one way or the other[65] – was not the sole cause of his conspiring: "wounded pride and fierce ambition" played a great role in his decision-making.

[66] Many of the senatorial members of the conspiracy were men who had been ejected from the senate for immorality, corruption, or seen their careers stall out (especially in attempts to reach the consulship).

[67] The men who joined Manlius' rebellion were largely two groups: poor farmers who had been dispossessed by Sulla's confiscations after the civil war and ruined Sullan veterans seeking more riches.

[68] Cicero, in his invectives, naturally focused on the ruined Sullan veterans, who were unpopular; but at the end, Catiline likely kept only the support of the dispossessed Etruscans who had "nowhere else to go".

[71] On 6 November, Catiline held a secret meeting in Rome at the house of Marcus Porcius Laeca where he planned to go to Manlius' army, for other members of the conspiracy to take charge of the nascent revolts elsewhere in Italy, for conspirators in Rome to set fires in the city, and for two specific conspirators to assassinate Cicero the next morning.

[75] On his departure, he sent a letter to his old friend and ally Quintus Lutatius Catulus Capitolinus, which Sallust copied into Bellum Catilinae.

[76] In the letter, Catiline defends himself as an injured party who took up the cause of the less fortunate in accordance with his patrician forebears' custom; he vehemently denies that he goes into exile due to his debts and commits his wife Orestilla to Catulus' care.

When news of this reached Rome, the senate declared Catiline and Manlius hostes (public enemies) and dispatched Antonius at the head of an army to subdue him.

[84] Antonius kept his men relatively docile near Faesulae, but after he received reinforcements from then-quaestor Publius Sestius in the last days of December, he moved out.

[85] On the day of the battle, Antonius gave operational command to Marcus Petreius (Sallust claims he was stricken with gout[86]), an experienced lieutenant,[87] who broke through the Catilinarian centre with the praetorian cohort, forcing Catiline's men to flight.

But Catiline was found far in advance of his men amid a heap of slain foemen, still breathing slightly, and showing in his face the indomitable spirit which had animated him when alive.

In Tuscany, a mediaeval tradition had Catiline survive the battle and live out his life as a local hero; another version gives him a son, Uberto, who eventually spawns the Uberti dynasty in Florence.

The first major attempt was Edward Spencer Beesly in 1878, who argued against the then-prevailing view that Catiline was "a demon breathing murder, rapine, and conflagration, with bloodshot eyes and pallid face, luring on weak and depraved young men to the damnation prepared for himself".

[101] Seager's defence does not go so far, but instead argues the conspiracy was purposefully incited by Cicero and the senate to purge Italy of men who might join with Pompey if he were to follow in Sulla's footsteps on his then-imminent return from the Third Mithridatic War.