<p>The green synthesis of metal nanoparticles (NPs), particularly silver (Ag), gold (Au), copper (Cu), and iron (Fe), has attracted considerable attention owing to their inherent biocompatibility, low toxicity, and tunable physicochemical properties. These features make them highly promising for diverse biomedical and environmental applications. In this study, we investigate the synthesis of these four metallic NPs using environmentally sustainable reduction techniques and comprehensively evaluate their biological activities, with particular focus on anticancer and antibacterial properties. Their potential roles in therapeutic interventions, drug delivery systems, and antimicrobial applications are highlighted. In addition, we discuss the growing demand for eco-friendly nanotechnology in food packaging, where such green-synthesized NPs can be effectively employed. Conventional nanoparticle synthesis methods, which rely on synthetic chemicals and physical processes, often pose environmental and health risks. In contrast, the use of plant extracts or metabolites for the synthesis of Ag, Au, Cu, and Fe NPs offers a safer, more economical, and readily accessible alternative, consistent with the principles of sustainable chemistry, which aim to minimise harmful by-products. The notable antimicrobial efficacy and non-toxic nature of these green-synthesized NPs position them as valuable components in sustainable food packaging solutions. Overall, this research emphasizes the importance of environmentally benign synthesis routes for producing nanoparticles with enhanced biological functionalities, thereby contributing to the development of sustainable and efficient strategies in both biomedicine and food technology.</p>