Green science has been witnessed in the advancement with nanobiotechnology enriched with nature-associated biogenesis of nanoparticles over the last three decades. Noble elements, including gold and silver, are the most promising developing trend in nanotechnology for designing bioengineering materials that might be used as modern diagnostic instruments and tools to combat major diseases. Silver and gold nanoparticles possess strong antimicrobial, antioxidant, cytotoxic and anticancer properties that enable the development of new processes with enhanced and target-specific actions. Siver and gold nanoparticles were synthesized using Prawn Head Extract (PHE) and characterized in a previous study. The objective of the present work was to investigate the antioxidant, cytotoxicity and anticancer activity of biosynthesized nanoparticles. The antioxidant properties were analysed by the DPPH(2,2-diphenyl-1-picryl-hydrazyl-hydrate) assay, and the IC50 values were 1020 μg/mL for silver nanoparticles and 649 μg/mL for gold nanoparticles. The in vitro cytotoxicity of the vero cell line and anticancer activity in a human breast cancer cell line (MCF-7) were determined using the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) assay. The cytotoxicity assay revealed IC50 values of approximately 118.75 and 93.75 μg/mL in silver and gold nanoparticles, respectively. The anticancer activity in the human breast cancer cell line MCF-7 showed IC50 values of approximately 93.75 and 46.8 μg/mL in silver and gold nanoparticles, respectively. The MTT assay, microscopic examination and DNA fragmentation assays confirmed morphological changes, membrane damage, cell shrinkage and mortality. Conclusively, the study revealed dose-dependently promising effects and can be further exploited in the field of biomedicine as a potential source with a standardized protocol for application.