Natural enzymes play a pivotal role in catalyzing essential biochemical reactions in both and systems, owing to their exceptional catalytic efficiency, substrate specificity, and biocompatibility. However, their widespread application is significantly limited by inherent drawbacks such as high production costs, limited operational stability, and poor reusability. In response, two-dimensional (2D) nanomaterials, such as graphene, borophene, hexagonal boron nitride (h-BN), transition metal dichalcogenides (TMDs), and MXenes, have emerged as a novel class of enzyme mimetics, or nanozymes, offering distinct advantages due to their atomic thickness, high surface-to-volume ratio, and tunable electronic and physicochemical properties. These materials exhibit superior stability, cost-effectiveness, and structural versatility, making them well-suited for applications across biomedical and environmental domains. In this review, we comprehensively discuss recent advances in the design and functionalization of 2D nanozymes with metallic nanoparticles, single-atom catalysts, and metal oxides, emphasizing their catalytic mechanisms and enzyme-mimetic behaviors. We further examine their utility in biomedical applications, including biosensing, bioimaging, therapeutic diagnostics, and regulation of oxidative stress, as well as in environmental applications such as pollutant detection and remediation. Finally, we highlight current challenges and outline future research directions toward the development of next-generation 2D nanozymes with enhanced functionality and translational potential in healthcare and environmental sustainability.