Two-dimensional metallic transition metal dichalcogenides (2D TMDs) such as 1T phases of MoS2 and WS2, NbS2, TaS2 and VS2 have been studied as potentially inexpensive and earth abundant electrocatalysts for the hydrogen revolution reaction (HER). The performance of HER catalysts is typically evaluated in terms of overpotential at which the reaction starts and the Tafel slope – a measure of the over-potential required to increase a reaction by a factor of 10. The overpotential and Tafel slope values of metallic phases and edges9 of 2D TMDs approach those of Pt nanoparticles – the best HER catalyst. However, despite substantial progress the overall current density of 2D TMD catalysts remains orders of magnitude lower (~ 10 – 100 mA-cm-2) than industrial Pt and Ir electrolyzers (> 1,000 mA-cm-2) 10,11. Here, we report the synthesis of three dimensional (3D) niobium disulfide (Nb1+xS2 where x is ~ 0.35)12 as a HER catalyst that is capable of evolving hydrogen at current densities of > 5,000 mA-cm-2 at an overpotential of ~420 mV versus reversible hydrogen electrode (RHE). We find the exchange current density at 0 V for 2H phase Nb1.35S2 catalysts to be ~ 0.8 mA-cm-2 (comparable to that of noble metals), corresponding to a turnover frequency of ~ 0.2 s-1. We demonstrate a proof of concept electrolyzer based on 2H Nb1.35S2 cathode that is capable of generating current densities of 1000 mA-cm-2. Our theoretical results reveal that the Nb1.35S2 with Nb terminated surface has free energy for hydrogen adsorption that is close to thermoneutral, facilitating HER. The Nb1+xS2 could therefore be a viable non-precious metal catalyst for practical electrolyzers used to generate hydrogen.