Thermal fiber drawing process has emerged as a promising nanomanufacturing process to generate high-throughput, well aligned, and indefinitely long micro/nanostructures. However, scalable fabrication of metal–polymer nanocomposite is still a challenge, since it is still very difficult to control metal core geometry at nanoscale due to the low-viscosity and high-surface energy of molten metals in cladding materials (e.g., polymer or glass). Here, we show that a scalable nanomanufacture of metal–polymer nanocomposite via thermal fiber drawing is possible. Polyethersulfone (PES) fibers embedded with Sn nanoparticles (<200 nm) were produced by the iterative size reduction thermal fiber drawing. A post-characterization procedure was developed to successfully reveal the metal core geometry at submicron scale. A three-stage control mechanism is proposed to realize the possible control of the metal nanoparticle morphology. This thermal drawing approach promises a scalable production of metal–polymer nanocomposite fibers with unique physicochemical properties for exciting new functionalities.