In this article, conductive composite films based on TEMPO-oxidized cellulose nanofibers (TOCN) and polypyrrole (PPy) were synthesized in situ by a Chemical Polymerization Induced Adsorption Process of pyrrole on the surface of TOCN in aqueous medium. Resulting composite films were investigated by X-ray photoelectron spectroscopy, scanning, and transmission electron microscopy, N-2 gas adsorption analysis, thermogravimetric analysis, mechanical tests, and conductivity measurements in the ambient air. Our results showed a stable, flexible, and highly electrically conductive composite film in which PPy nanoparticles coated the surface of the TOCN network. In addition, the advantage in using the famous material, TOCN, is clearly due to the presence of carboxylate (COOH/COO-Na+) and hydroxyl (OH) moieties on the surface of TOCN. These reactive moieties could enhance the adsorption process of positively charged PPy backbone during polymerization. TEM observations demonstrated the formation of a PPy coat along the surface of the cellulose nanofibers having a diameter of about 90 nm which is relatively higher compared to the initial diameter of pure TOCN (similar to 9 nm). Despite the physical and chemical treatment of TOCN during polymerization, the micrometric length of the cellulosic nanomaterial was maintained. In addition, the incorporation of polyvinyl alcohol as an additive in the TOCN/PPy composite seems to enhance the flexibility of composite films (bent up to 180A degrees) without losing the high electrical conductivity. Finally, because of the high conductivity and good mechanical properties of the TOCN/PPy composite films obtained in this work, they can be used as a promising material in applications of sensors, flexible electrodes, and other fields requiring electrically conductive flexible films.