A systematic investigation of catalytic activity of boron phosphide nanowire (BP NW) towards over-all water-splitting reaction has been performed by evaluating the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) activities. Intended to the mentioned aim, we have utilized Kohn-Sham formulated extensively popular ab initio method based on density functional theory (DFT). The structural and electronic properties of the BP NW are computed and compared with its bulk phase. We observe dramatic indirect to direct bandgap transition with pronounced energy gap after introducing two-dimensional confinement that is akin to the other reported III-V NWs. The calculated partial density of states with van Hove singularity also confirms the same. Owing to its moderate bandgap value, the applicability of the BP NW as an HER/OER catalyst is assessed by computing the site dependent HER/OER activities. Our computation on Gibbs free energy for the case of hydrogen adsorption with -1.19 eV magnitude gives better results; whereas in case of OER, the results with higher magnitude of Gibbs energy implicate over binding of oxygen with adsorbent thus revealing non-feasible desorption of oxygen from adsorbent. Significant perturbation in electronic states of NW under hydrogen adsorption confirms high sensitivity of BP NW for hydrogen adsorption. Further, the effect of substitutional doping on HER and OER activities suggests that the doped NW shows poor HER activity in contrast to the site-dependent better OER activity in case of Ga doped BP NW. The present BP NW shows potential as an HER catalyst owing to its lower adsorption and Gibbs free energies (-1.07 and -0.84 eV), as compared to previously conventionally utilized III-V NWs. Henceforth, we believe that the present study would serve as a blueprint for the researchers to design and develop toxic and/or metal-free catalyst that can be utilized for efficient water-reduction. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.