We report the electrochemical charge storage performance of NiSb2O6, obtained through a solid-state reaction method, and a detailed comparison with its reduced graphene oxide composite. Intriguingly, the composite, NiSb2O6-reduced graphene oxide, yielded a large capacitance of 952.38 F g-1, at a mass-normalized-current of 1 A g-1, which is at least 4-fold higher than that of the bare NiSb2O6. We have also tested the performance of the composite in a two-electrode symmetric device. The NiSb2O6-reduced graphene oxide symmetric device showed an excellent capacity retention of ∼94%, even after 10 000 cycles. We conducted comprehensive density functional theory (DFT) simulations to determine the structure and electronic characteristics of NiSb2O6, and the composite material of NiSb2O6-reduced graphene oxide. The incorporation of reduced graphene oxide results in an augmentation of electronic states near the Fermi level, hence showing an improvement in the conductivity of the hybrid system. The composite structure exhibits a lower diffusion energy barrier for electrolyte ions and a greater quantum capacitance than pristine NiSb2O6. These characteristics confirm our experimental findings and justify the observed improvement in charge storage performance for the composite structure. Based on the results obtained, it can be concluded that the combination of rGO and NiSb2O6 displays excellent performance and has the potential to serve as a highly efficient material for electrochemical capacitors.