Herein we report a facile and direct synthesis of porous NiCo₂O₄ nanowire arrays (NWAs) with robust mechanical adhesion to conductive electrodes by a simple two-step method. Upon complete pyrolysis of the cobalt–nickel-hydroxide precursor, high-quality crystalline NiCo₂O₄ is achieved. The porous NiCo₂O₄ nanowires were found to be highly active for catalytic water oxidation when serving as the working electrodes without any external materials (binder and/or carbon black), as evidenced by exhibiting higher catalytic current density for water oxidation compared to precious metal oxide catalysts such as iridium oxide (IrO₂) under the same conditions and appreciable catalytic wave at ∼1.52 V (vs. RHE). The optimal performance of the as-synthesized NiCo₂O₄ nanowires showed a current density of 10 mA cm⁻² under an overpotential of only 0.46 V and 20 mA cm⁻² under an overpotential of 0.72 V, corresponding to a Faradaic efficiency of nearly 100%. The atomic-scale analysis of the NiCo₂O₄ nanowires was further conducted by spherical-aberration-corrected transmission electron microscopy (TEM). The highly exposed high-index facets and one-dimensional (1D) configuration of the as-synthesized porous NiCo₂O₄ nanowires may be responsible for the high catalytic performance of water oxidation, which exhibit excellent activity and unique advantages for catalytic water splitting.