He was probably born between 125 and 123 BC. In 90 BC, during the Social War, Curio was a tribune of the plebs. From 87 BC until 81 BC he served as a legate under Lucius Cornelius Sulla; First in Greece and Asia during Sulla's campaigns against king Mithridates of Pontus then against the Cinna-Marius faction during the Civil War of 83-81 BC. During the First Mithridatic War he besieged the Athenian tyrant Aristion, who had taken position on the Acropolis, during the Siege of Athens.