 Sallust describes him as a military man, who in 62 BC already had a thirty-year-long career in the army as Military tribune, Prefect and Legate behind him.Petreius served at the latest in 64 BC as Praetor, although the exact year he took on this position is unknown.Petreius first served under Pompeius Strabo during the Social War (91-88 BC).