The first Catilinarian conspiracy was a plot to murder the consuls of 65 BC and seize power. Historians consider it unlikely that Catiline would have been involved in the first Catilinarian conspiracy or, indeed, that the conspiracy existed at all.
In all likelihood, Catiline was not involved in the so-called first Catilinarian conspiracy, although several historical sources implicate him in it. There does not seem to be a single account that is represented in all of the sources: rather, it seems that the accounts represent a collection of rumors accusing different political figures in attempts to tarnish their names. As it pertains to Catiline, much of the information originates in Cicero’s speech In Toga Candida which was given during his election campaign in 64 BC. Only fragments of this speech still exist, in the later writing of Asconius Pedianus.
The consuls-designate, Publius Autronius Paetus and Publius Cornelius Sulla, were prevented from entering office because of ambitus, electoral corruption, under the Lex Acilia Calpurnia. Thus, the two other leading candidates, Lucius Manlius Torquatus and Lucius Aurelius Cotta, were elected in a second election and were to enter office on January 1, 65 BC. Supposedly, Catiline, incensed because he was not allowed to stand for the consulship, conspired with Gnaeus Calpurnius Piso and the former consuls-designate to slaughter many of the senators and the new consuls the day they assumed office. Then they would name themselves the consuls for the year and then Piso would have been sent to organize the provinces in Hispania. Alternatively, Suetonius claims that Julius Caesar and Marcus Licinius Crassus directed the conspiracy, but he fails to mention Catiline's involvement. Instead of assuming the consulship, Crassus is accused of planning to become dictator and intending to name Caesar magister equitum.