Vanadium redox flow battery (VRFB) is one of the most promising technologies for large-scale energy storage application owing to its various gorgeous features, such as long cycle life, high safety, and flexible design. In this study, potentially cost-effective and powerful tungsten oxide nanowire-decorated graphite felt (WO_x NW-GF) was successfully synthesized for VRFB application via a simple hydrothermal route followed by annealing. The GF electrode decorated with WO_x NW as a catalyst revealed an excellent electrochemical activity and reversibility toward the VO^2+/VO₂⁺ redox reaction. A VRFB cell assembled with the WO_x NW-GF electrode exhibited superior energy efficiency of 80% with a current density of 80 mA cm⁻², which is around 12% more efficient than that of the cell assembled with treated GF. The enhanced performance of a VRFB was attributed to the presence of oxygen vacancies on the tungsten oxide, which were proven to serve as active sites for the VO²⁺/VO₂⁺ redox reaction. Furthermore, the uniformly distributed nanowires on the surface of graphite felt facilitated the charge transport process, enhanced wettability and electrolyte accessibility, and thus remarkably reduced electrochemical polarization during the mass transfer of active species. The long-term cycling test verified the outstanding stability of the tungsten oxide-based catalyst with negligible performance decay even after 100 cycles.