The widespread usage of electronic devices and wireless technologies has made way to concerns about electromagnetic interference (EMI), that can interrupt the operation of such devices and endanger human health, if appropriate shielding measures are not implemented. While conventional metal materials are often used for EMI shielding applications due to the inherent conductivity they offer, their limitations in terms of weight, susceptibility to corrosion, reflection of EM waves leading to secondary EM wave pollution and difficulty in application to structures with complex geometries have prompted the search for alternatives. This study presents bio-inspired, ultrathin (4-5 μm), free-standing, and flexible nanocomposite films composed of Ti3C2Tx MXene and Nanocrystalline Cellulose (CNC), developed via vacuum-assisted filtration. These films exhibit a nacre-like layered architecture, promoting interfacial polarization and multiple internal reflections that enable absorption dominant shielding. At 90 wt.% MXene content, the films achieved an EMI shielding effectiveness (EMI SE) of 44 dB, a high electrical conductivity of 1465.25 S cm-1, and a low density of 3.41 g cm-3. The specific shielding effectiveness (SSE) and absolute effectiveness (SSEt) reached 12.92 dB cm³ g⁻¹ and 27,247.05 dB cm2g-1, respectively. Notably, even at just 10 wt.% MXene, the EMI SE was observed to be at 25 dB, surpassing the 20 dB commercial benchmark. The combination of highly conductive, layered MXene with sustainable CNC enhance mechanical robustness and introduce nanoscale insulating gaps that favor absorption dominant EMI shielding. These nanocomposites demonstrate promising potential for next-generation wearable, flexible, and miniaturized electronics requiring robust, sustainable, and lightweight EMI shielding.