Wearable electronics require sustainable, high-performance energy harvesting from irregular mechanical stimuli; however, biodegradable materials often lack durability and output for practical applications. In this study, we developed glutathione-functionalized cellulose (CF-Gx, x = 0.5, 1, 2, 3, or 4 wt% glutathione) composite films to fabricate a biodegradable triboelectric nanogenerator (TENG) that efficiently harvests energy for wearable devices. Glutathione reinforced the cellulose matrix via extensive hydrogen bonding, forming a stable intermolecular network that enhanced mechanical integrity and triboelectric performance. Fabricated via a scalable solution-casting process, the optimized CF-G2-based TENG achieved a peak-to-peak voltage of up to 798.8 V (with an average of approximately 776 V) under manual operation—more than double the 346 V recorded under automated operation—owing to dynamic friction and residual vibrations, making it ideal for wearables driven by intermittent forces. The TENG maintained a robust output despite exposure to artificial sweat, demonstrating its durability for skin contact scenarios. When integrated into a gesture-recognition system, it enabled wireless control via wrist movements, highlighting its potential for use in smart human–machine interfaces. Biodegradability was confirmed through cellulase immersion and soil burial tests; glutathione facilitated molecular diffusion and accelerated decomposition without causing ecological harm, as evidenced by healthy basil plant growth in CF-G2-degraded soil. These results indicate that CF-Gx films are a scalable, eco-friendly solution for next-generation wearable energy harvesters, bridging the gap between performance and sustainability in wearable electronics.