Catiline served under Pompey's father in the Social War of 89 and acquired an unsavoury reputation as a zealous participant in Sulla's proscriptions, killing his own brother-in-law during them. He was acquitted of charges of fornication with a Vestal Virgin in 73 and afterward became praetor in 68 and governor of the province of Africa in 6766. Because Catiline was then under prosecution for extortion, a charge of which he was eventually acquitted, he could not stand for the consular elections of 65 or 64. Later there was talk that he had planned to murder the consuls and seize power early in 65, but there is no solid evidence for this "first Catilinarian conspiracy." In 64 Catiline failed to be elected consul when Cicero was one of the successful candidates, and a year later he was again defeated for that office. Upon this last defeat, Catiline began to systematically enlist a body of supporters with which to stage an armed insurrection and seize control of the government. His proposals for the cancellation of debt and the proscription of wealthy citizens and his general championship of the poor and oppressed appealed to a variety of discontented elements within Roman society: victims of Sulla's proscriptions who had been dispossessed of their property, veterans of Sulla's forces who had failed to succeed as farmers on the land awarded to them, opportunists and desperadoes, and aristocratic malcontents.
Cicero, who was consul in 63, was kept fully informed of the growing conspiracy by his network of spies and informers, but he felt unable to act against the still-popular and well-connected Catiline. On October 21, however, Cicero denounced Catiline to the Senate in an impassioned speech, charging him with treason and obtaining from the Senate the "ultimate decree," in effect a proclamation of martial law. Catiline withdrew from Rome on November 8 and joined his army of destitute veterans and other supporters that had been collected at Faesulae in Etruria. Despite these events, the Senate remained only partly convinced of the immediate danger that Catiline represented. On December 3, however, some envoys of the Gallic tribe of the Allobroges, whose support had been imprudently solicited by important Catilinarian conspirators in Rome, provided Cicero with a number of signed documents that unmistakably proved the conspiracy's existence. These suspects were arrested by Cicero and were executed on December 5 by decree of the now-thoroughly alarmed Senate. The Senate also mobilized the republic's armies to take the field against Catiline's forces.
Catiline, assuming charge of the army at Faesulae, attempted to cross the Apennines into Gaul in January 62 but was engaged by a republican army under Gaius Antonius Hybrida at Pistoria. Fighting bravely against great odds, Catiline and most of his followers were killed.
(Encyclopedia Britannica)
In the late Roman Republic, an aristocrat who turned demagogue and made an unsuccessful attempt to overthrow the republic while Cicero was a consul (63).