[5] As consul in 63 BCE, Cicero had revealed the conspiracy of Lucius Sergius Catilina (Catiline), a failed consular candidate who had attempted to seize power in a coup.

[10] Cicero's political enemy, Publius Clodius Pulcher, passed a law as tribune in February 58 BCE condemning anyone who had executed Roman citizens without a trial.

[7] In 61–60 BCE, Cicero had represented an association (societas) of tax-collectors, including Plancius's father,[d] in their attempt to reduce their financial obligations to the Roman state.

[17] When the exiled Cicero arrived at Dyrrachium in western Greece late in April 58 BCE, Plancius was serving as a quaestor (a junior financial official) on the staff of Lucius Appuleius Saturninus, the governor of Macedonia.

[17] He then successfully ran for curule aedile in 55 BCE,[22] in an election that Lily Ross Taylor has described as "a travesty of Roman free institutions".

[31] Like Cicero, Laterensis had been an early opponent of the triumvirs – he had withdrawn his candidacy for tribune in 59 BCE, because those elected were obliged to swear to uphold the laws of Julius Caesar.

[32] Laterensis made the prosecution a few weeks after the election of 54 BCE:[33] the trial was held around the time of the ludi Romani, which took place in late August or early September.

[34][e] The prosecution was made under the lex Licinia de sodaliciis, a law put forward by the triumvir Marcus Licinius Crassus in 55 BCE.

[31] Laterensis's arguments appear to have generally been more appropriate to a trial for conventional ambitus than one de sodaliciis ('concerning sodalicia'), and Cicero argued that he had only made his prosecution under the lex Licinia to benefit from its distinctive jury-selection procedure.

[44] Andrew Lintott has suggested, following an argument presented by Jules Humbert in 1925, that the transmitted text of the speech may combine parts of different orations given by Cicero at different points in the trial.

[47] Cicero accepts that Plancius had made use of sodalitates (political associations), but argued that they were merely groups of friends, aimed at mutual support rather than to improperly influence the election.

Cicero had previously used this tactic extensively in three speeches, and would do so again in the Pro Ligario of 46 BCE, but it is not attested elsewhere in Roman oratory or in Greek rhetorical manuals.

[62] Cicero twice uses the device of sermocinatio, an imagined dialogue with an interlocutor, following the practice of contemporary rhetoricians in using it to add interest and persuasive power to his speech.

[64] Elsewhere in the speech, he makes possible allusions to two other works of early Latin literature: the Annales, a historical epic poem by Ennius, and the Satires of Gaius Lucilius.

[72] In December of the same year, Cicero drew on the arguments he had made in the Pro Plancio in a letter to Publius Cornelius Lentulus Spinther, defending his collaboration with the triumvirs.

[75] The second-century author Aulus Gellius mentions it twice in his Attic Nights, a miscellany of notes on various scholarly topics, to illustrate Cicero's use of rhetoric and grammar.

[77] Unlike most of the surviving speeches of Cicero, the Pro Plancio was not used or quoted in the manuals of rhetoric published during the Roman period and late antiquity.

[79] An ancient commentary (scholia) on the Pro Plancio was preserved in the Bobbio palimpsest (Codex Ambrosianus), a late fifth-century manuscript overwritten in the seventh century with an account of the Council of Chalcedon.

Both T and E probably derive their texts of the Pro Plancio from a single original, which in turn probably descends from an edition of Cicero's works made in the ninth or tenth century.