Titus Labienus (c. 100 BC - March 17, 45 BC) was the most important member of a Roman family said (without authority) to belong to the gens Atia. He is remembered as one of Caesar's lieutenants, mentioned frequently in the accounts of his military campaigns.

His early service was ca. 78-74 in Cilicia under Servilius.

In 63 BC, at Caesar's instigation, Labienus prosecuted Gaius Rabirius for treason; in the same year, as tribune of the plebs, he carried a plebiscite which indirectly secured for Caesar the dignity of pontifex maximus (Dio Cassius xxxvii. 37). He served as a legatus throughout Caesar's Gallic campaigns and took Caesar's place whenever he went to Rome.

His chief exploits in Gaul were the defeat of the Treviri under Indutiomarus in 54, his expedition against Lutetia (Paris) in 52, and his victory over Camulogenus and the Aedui in the same year. On the outbreak of the civil war (49), however, he was one of the first to desert Caesar, apparently resentful at lack of recognition.

He was rapturously welcomed on the Pompeian side; but he brought no great strength with him, and his ill fortune under Pompey was as marked as his success had been under Caesar. From the defeat at the Battle of Pharsalus, to which he had contributed by affecting to despise his late comrades, he fled to Corcyra, and thence to Africa. There he was able by mere force of numbers to inflict a slight check upon Caesar at the Battle of Ruspina in 46. After the defeat at the Battle of Thapsus he joined the younger Pompey in Hispania, and was killed at Munda.

His son was Quintus Labienus .

Another Titus Labienus was an orator and historian in the time of Augustus Caesar, nicknamed Rabienus for his vigorous style. He killed himself when the Senate had his books burned. Caligula later overrode the Senate and had the books restored.