He led the Senatorial forces in the victory over the revolutionary Lucius Sergius Catilina at Pistoria in early 62 BC, while Hybrida remained away from the battle with a foot ache.
[4] From 55 BC, Petreius and Lucius Afranius administered the Spanish provinces as Legates, while the official governor Gnaeus Pompeius Magnus remained in Rome.
[5] After the outbreak of the Civil War in 49 BC, Petreius and Afranius marched against Caesar, who for his part wished to secure Spain before moving against Pompey in Greece.
[6] The two Legates suffered defeat after initial successes, and were forced to capitulate and disband their army on August 2 at Ilerda.
After Pompey's defeat in the Battle of Pharsalus, Petreius and Cato fled from the Peloponnese to North Africa, where the former continued to serve as Legate in the resistance to Caesar.