Through his mother's first marriage to Pontifex Maximus Quintus Mucius Scaevola he was the half-brother of Mucia Tertia the later wife of Pompey the Great.
[6] Nepos' first recorded public activity was to bring charges in 72 BC against Gaius Scribonius Curio, who was a family rival.
[8] Like his brother, Metellus Celer, he served in the Third Mithridatic War against Mithridates VI of Pontus and Tigranes the Great of Armenia, taking Damascus in Syria in 64 and leaving Pompey's army for Rome the next year to stand for the tribunate as a Pompeian ally.
[11] He tried to indict Cicero on charges of murder, but the senate passed an amnesty for the consul and then threatened to declare any potential prosecutor a public enemy.
Nepos likely heard from his brother – Metellus Celer, then proconsul in Cisalpine Gaul, – that Catiline would imminently be defeated by Antonius Hybrida's forces in northern Italy.
[15] Nepos, along with his ally Julius Caesar (then serving as praetor), assembled the tribes at the Forum before the Temple of Castor and Pollux.
[17] In response to the violence, the senate passed a senatus consultum ultimum against Nepos, forcing him to flee the city to Pompey's camp in the east.
[20] The proposal to send Pompey after the Catilinarians, regardless, became irrelevant when Catiline and his forces were decisively defeated in battle at Pistoria shortly thereafter.
[22] The move likely was related to reforms, pursued by the senate in the aftermath of the Catilinarian conspiracy, to buttress support among agricultural exporters and wealthy importers of luxury goods.
Writ large, the alliance between Pompey, Caesar, and Crassus forced a realignment in Roman politics with many factions shifting to balance against the triumvirs.
[26] Pompey and Spinther were eventually able to convince Nepos to drop his opposition and had a bill recalling Cicero ratified by the comitia centuriata.