After its surrender, he joined Pompey in Greece and was slain in the flight after the battle of Pharsalus, in which he commanded the right wing against Antony (Caesar, Bellum Civile, i., ii., iii.; Dio Cassius xxxix., xli.; Appian, B.C. ii.
Gnaeus Domitius Ahenobarbus, son of the above, accompanied his father at Corfinium and Pharsalus, and, having been pardoned by Caesar, returned to Rome in 46.
In 48 B.C. during the civil war he commanded his father's fleet in the Adriatic. After the battle of Pharsalus he set out for Africa with the remainder of the Pompeian party, but, meeting with little success, crossed over to Spain.
Deputy-governor of Italy during Caesar's absence in Spain (49), second in command in the decisive battle of Pharsalus (48), and again deputy-governor of Italy while Caesar was in Africa (47), Antony was second only to the dictator, and seized the opportunity of indulging in the most extravagant excesses, depicted by Cicero in the Philippics.
On the outbreak of the civil war between Pompey and Caesar, Quintus, like Marcus, supported Pompey, but after Pharsalus he deserted and made peace with Caesar, largely owing to the intercession of Marcus.