Leontius the Mechanic was a technical author of the 5th–6th century CE. His existence is known only from his sole surviving treatise, which identifies him as a practitioner of engineering, architecture, or military mechanics. His work reflects the continuity of Hellenistic and Roman engineering traditions into the early Byzantine period.

His only known work is the Poliorketika, a treatise on siege engines and artillery. Leontius is significant as a representative of the practical literature that transmitted ancient mechanical knowledge. His Poliorketika forms part of the tradition of military manuals and serves as a witness to the state of military technology and applied engineering practice during Late Antiquity.