This study investigates the dual functionality of Tannic Acid (TA), a bio-derived polyphenol, as a surface modifier for ultra-high molecular weight polyethylene (UHMWPE) fibers and as a hardener for diglycidyl ether of bisphenol A (DGEBA) epoxy resin, aimed at enhancing composite laminate performance and sustainability. The surface characteristics of UHMWPE fibers were investigated by Fourier transform infrared spectroscopy and scanning electron microscopy. The TA-modified fibers exhibited functional groups that enhanced their polarity and improved their compatibility with the epoxy matrix. Furthermore, thermogravimetric analysis revealed an increase in thermal degradation onset from 336°C to 357°C after TA treatment. The hand lay-up method was used to manufacture composite UHMWPE laminates impregnated with TA-hardened resins at different TA concentrations. Cone calorimetry results revealed improved fire resistance for TA-loaded composites, with a 44% reduction in peak heat release rate (PHRR) respect to the control sample, as well as a better fire performance index. Composite laminates manufactured with TA-modified fibers and TA-hardened resin demonstrated up to 45% improvement in tensile strength.