Gnaeus Domitius Ahenobarbus, a member of the noble Ahenobarbus family, accompanied his father at Corfinium and Pharsalus, and, having been pardoned by Julius Caesar, returned to Rome in 46 BC.

After Caesar's assassination he attached himself to Marcus Junius Brutus and Cassius, and in 43 BC 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 BC. 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 BC). He died soon afterwards (Dio Cassius xlviii.-l; Appian, Bell. Civ. iv., v.).

His son Lucius Domitius Ahenobarbus was married to Antonia Major, daughter of Mark Antony. They became parents to a younger Gnaeus Domitius Ahenobarbus and grandparents of the Roman Emperor Nero.