Terahertz (THz) spectrum and technology are envisioned to be a highly promising solution for enabling 6G and beyond wireless networks. This demand coincides with an urgent need to develop efficient electromagnetic interference shields to alleviate electromagnetic pollution in the THz range. Fully bioderived THz shields could be a sustainable solution to transcend towards a biocarbon economy. Herein, we report an environmentally benign and facile approach to fabricating 3D porous ultra-light aerogels and flexible nanopapers from cellulose nanofibers and highly conductive biocarbon fully derived from biomass. These functional constructs showcased excellent broadband THz shielding performance in both sub THz (W band) and THz region (0.4–2.0 THz). The THz shielding effectiveness of a 600 µm thick nanopaper and 3.00 mm aerogel was found to be 46 dB and 70 dB, with superior THz absorption behaviour and minimal reflection of THz signals. The electronic structure and charge transfer properties were examined under an external electric field based on density-functional theory. The results show that the effect of the external electric field induces intramolecular charge transfer from the lower-graphitic sheet to the upper-graphitic sheet of the nanocomposite suitable for THz excitation. Moreover, these sustainable absorbers could deliver similar THz shielding performance compared to graphene foam (74 dB), exemplifying their humungous potential as advanced functional materials for futuristic THz devices.