Quintus Labienus (died 39 BC), the son of Titus Labienus, was a Roman republican general, later in the service of Parthia.
After Julius Caesar was murdered in 44 BC, Labienus took the side of Brutus and Cassius, the latter whom he served in the capacity of an ambassador to the Parthians. After Brutus and Cassius were defeated at Philippi, Labienus joined the Parthians.
When the Parthians invaded the Roman territories in 40 BC they were led by Pacorus and Labienus. The Parthian army crossed the Euphrates and attacked Apamea. The attack on Apamea failed but Labienus was able to entice the Roman garrisons around Syria to rally to his cause. The combined Romano-Parthian army then proceeded to defeat Mark Antony's governor L. Decidius Saxa in a pitched battle and took Apamea. After the Roman defeat at Apamea, the Parthians split their army. Pacorus turned south and conquered the Levant from the Phoenician coast through Palestine. Labienus turned north to follow Saxa, whom he defeated and killed in Cilicia. Labienus then proceeded to conquer all of Asia Minor. Under Labienus and Pacorus, the Parthians had restored their territory to nearly the limits of the old Achaemenid empire and controlled all of Asia Minor except for a few cities but the Parthian successes were not long-lasting. In 39 BC, a Roman counterattack under Publius Ventidius in Asia Minor defeated Labienus, who was subsequently captured and executed. One year later Pacorus too was killed in Syria.