Abstract <p>This review discusses the application of the ionic liquid <i>N</i>-methylpyrrolidone hydrosulfate (NMP-HSO₄) in various chemical processes. As an acidic ionic liquid, NMP-HSO₄ has found broad application in organic transformations due to its unique catalytic properties and environmental advantages. The catalytic applications of NMP-HSO₄ are demonstrated in diverse reactions, including the Diels–Alder reaction, multicomponent Mannich reaction, esterification, glucose-to-biofuel conversion, desulfurization of petroleum fractions, and other chemical transformations. The authors specifically examine its role as a catalyst in the three-component Mannich reaction involving bicyclo[2.2.1]heptanol, secondary amines, and formaldehyde, noting significant improvements in product yield and catalytic efficiency. Furthermore, the potential of NMP-HSO₄ in petrochemical synthesis is explored, particularly in esterification of monobasic acids with various alcohols and the synthesis of phenol-formaldehyde resins. The advantages of using NMP-HSO₄ over traditional catalysts are highlighted, emphasizing its alignment with green chemistry principles, such as reduced environmental impact, improved efficiency, and sustainability. Additionally, its reusability, thermal stability, and ability to operate under mild reaction conditions make it an attractive choice for sustainable industrial applications. The integration of NMP-HSO₄ into catalytic systems contributes to resource efficiency, cost-effectiveness, and minimized waste generation, supporting the development of environmentally friendly chemical processes.</p>