After Caesar's assassination he attached himself to Marcus Junius Brutus and Cassius, and in 43 was condemned by the lex Pedia as having been implicated in the plot. He obtained considerable naval successes in the Ionian Sea against the Second Triumvirate, but finally, through the mediation of Gaius Asinius Pollio, became reconciled to Mark Antony, who made him governor of Bithynia.
He took part in Antony's Parthian campaigns, and was consul in 32. When war broke out between Antony and Octavian, he at first supported Antony, but, disgusted with his intrigue with Cleopatra VII of Egypt, went over to Octavian shortly before the battle of Actium (31). He died soon afterwards (Dio Cassius xlviii.-l; Appian, Bell. Civ. iv., v.).