Quintus Labienus Parthicus (died 39 BC), the son of Titus Labienus, was a Roman republican general, later in the service of Parthia. After the then main political power in Rome, Julius Caesar, was murdered by a conspiracy in 44 BC, Labienus took the side of the pro-republic conspirators, lead by Brutus and Cassius, the latter of whom he served in the capacity of an ambassador to the Parthians. After Brutus and Cassius fled east to Macedonia and were defeated there in the Battle of Philippi by Caesar's imperialist successors (the Second Triumvirate, particularly Mark Antony and Caesar's heir Octavian, the future emperor Augustus), Labienus joined the Parthians.