Vertically aligned 2D TMDC such as MoS₂ and WS₂ carry huge promise in many applications of nanometric architectures, due to their high aspect ratio and extensively exposed edges. The chemical active exposed edges with dangling bonds play an important role in many catalytic reactions like hydro desulfurization, hydrogen evolution reaction (HER). HER opens a pathway to next generation environment friendly energy production. But it is limited by scarcity and high price of essential Pt catalyst for large scale industrial application. Efforts have therefore been initiated to explore vertically standing 2D TMDs as promising substitutes of Pt. Main factors contributing to enhanced catalytic performance are i) increase in catalytically active sites in the exposed area, and ii) increase in catalytic performance of individual active sites. Maximization of active sites demands a control on vertical morphology to optimize length, thickness, and density of the flakes. Performance of individual active sites can be enhanced by identification and maximum exposure of the material responsible for catalytic activity. Metals being the active site for TMDs, vertical flakes should possess sulphur vacancy to expose the catalytic metal site, leading to a demand for controlling stoichiometry of the flakes. Clear understanding of the growth mechanism can provide such control on the desired growth. To meet this objective, we have explored CVD growth of WS₂ as functions of several process parameters using Tungsten hexacarbonyl [W(CO)₆] and hydrogen disulphide (H₂S) as precursors in hydrogen (H₂) ambient. Process parameters were first tuned to obtain morphology switching from horizontal layers to vertically aligned flakes. Length, density, thickness, composition and stoichiometry of the WS₂ flakes were then investigated systematically as functions of growth temperature T, total reactor pressure P, and flow rate η of the precursors. Annealing of selected films under various conditions were also explored to achieve stoichiometry desirable for enhanced catalytic performance. Here, we report vertical aligned WS2 nanosheets as efficient catalysts for hydrogen evolution with low overpotential of 220 mV at 10 mA cm−2 and a Tafel slope of 89 mV dec−1. Our results indicate that controlled growth vertical aligned WS2 nanosheets to obtain desirable performance is an suitable alternative to platinum for hydrogen evolution.