In this study, the synthesis of uncontaminated, dispersible, single-crystal, stoichiometric iron carbide (Fe$_3$C) nanoparticulate is pioneered successfully by using the flow-levitation (FL) method. The technique facilitates conditions forclean and direct iron-carbon gas-phase reaction at high temperature, and for the purpose of this work, production regimes and parameters were selected and customized in order to manufacture Fe$_3$C nanoparticles (NPs) of mean size 20 nm for subsequent characterization and evaluation. Characterization is performed using analytical techniques that include transmission electron microscopy (TEM/HRTEM/STEM), electron and X-ray diffraction, X-ray photoelectron spectroscopy, elemental CHNS analysis, specific surface area analysis and vibrating sample magnetometry analysis. The results confirm the uncontaminated and stoichiometric character of the iron carbide NPs and demonstrate their single-crystal nature. The synthesized product exhibits chemical inertness and excellent stability at room temperature over extended periods of time. A detailed analysis of magnetic properties of the nanoparticulate was also performed. The saturation magnetization (Ms) of the product was experimentally determined to be 124 A m$^2$ kg$^{–1}$, which is highly comparable to that of bulk iron carbide. The successful results merit to further investigate the clear advantages of the FL method to manufacture stoichiometric iron carbide nanoparticulate. The technique favours a significant level of parameter controllability during synthesis, which allows repeatability, and effective customization of size and magnetic properties of the resulting nanoproduct.