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The challenges imposed by climate change require the continued improvement and identification of materials for the development of green technologies. Point defect engineering is a promising technology for producing green hydrogen by taking advantage of catalytic hydrogen evolution reactions. In this work, we investigate the role of anionic and cationic vacancy point defects, as well as the nature of the active sites, in the catalytic activation of Cu2WS4 single layers. The stability of the pristine and defective structures of Cu2WS4 has been thoroughly investigated using density-functional theory calculations. A deep analysis of the formation enthalpy indicates that the Cu vacancy is the chemically most favorable vacancy. However, the calculated adsorption energy indicates that the presence of such vacancies slightly enhances the hydrogen evolution reaction. In contrast, the formation of an S vacancy considerably magnifies the same reaction in Cu2WS4 single layers.