ABSTRACT The study focused on the synergistic effect of cellulose nanofibrils (CNFs) as a lignocellulosic bionanomaterial and nickel-titanium (NiTi) alloy as a shape memory smart metallic material reinforcer on the thermal properties of sustainable smart composites. The casting process was used to produce composites with CNF loadings of 1%, 3%, and 5% and NiTi loadings of 3% into epoxy resin. Thermal properties were evaluated using thermogravimetric (TGA), derivative thermogravimetric (DTG), differential scanning calorimetry (DSC), and dynamic mechanical thermal (DMTA) analysis. The TGA results revealed that the CNF/NiTi-reinforced groups have considerable higher degradation temperatures and thermal stability than the control group. Also, at 800°C, CNF/NiTi-reinforced groups had a higher residual content than the control group. DTG results showed that the addition of CNFs decreased the degradation speed. Although the NiTi loading was constant, it was determined that the addition of CNFs increases the storage modulus (E′), loss modulus (E″), tan delta (Tan δ), and glass transition temperature (Tg). Overall, it can be concluded that CNF/NiTi-reinforced composites indicated significantly improved thermal stability, decomposition temperature, residual content, elastic, and viscous properties. These smart composites can be used for advanced material applications requiring thermal stability.