In recent days, 2-dimensional (2D) niobium disulfide (NbS2) with near-zero Gibbs free energy and superlative acid electrolyte stability has provoked a great deal of interest toward hydrogen evolution reaction (HER) electrocatalyst due to its active basal and edge sulfur sites. Herein, we developed a single step method for the direct deposition of 2D-NbS2 on high-aspect-ratio topographies of silicon nanowires (NWs) by chemical vapor deposition for the applications in HER electrocatalyst. The resultant 2D-NbS2 electrocatalyst demonstrates the HER overpotential of ∼74 mV vs RHE (reversible hydrogen electrode) @ 1 mA/cm2 under acidic conditions and stable for more than 20 h. More importantly, we developed the Si NWs array based photoelectrochemical water-splitting system with the direct deposition of 2D-NbS2 as HER catalyst. The resultant 2D-NbS2-Si NWs photocathode system demonstrates improved charge transfer characteristics at the Si-NbS2 interfaces that leads to an enhanced turn on potential (from 0.06 to 0.34 V vs RHE) with the current density of -28 mA/cm2 at the 0 V vs RHE. The results evidence the synergistic effect of 2D-NbS2 electrocatalysts that addresses poor surface kinetics of Si toward solar water electrolysis. Our comprehensive studies reveal NbS2 as a new class of photoelectrochemical cocatalyst for efficient solar HER performance by promoting the charge transfer process with prolonged acid stability.