<p>Bio-inspired synthesis of semiconducting nanoparticles has drawn extensive attention due to its eco-friendliness and suitable perspective. The current study is aimed at the synthesis of visible light-active ZnO nanoparticles using an aqueous extract of bio-waste of mango seeds to unveil their photocatalytic and antimicrobial potentials. The as-prepared ZnO nanoparticles showed a high degree of purity and crystallinity with 45.90&#xa0;nm of average size as confirmed by XRD results and demonstrated excellent optical absorbance in the visible range. Furthermore, the FESEM and TEM investigations revealed the spherical to polygonal morphology of ZnO nanostructures. The BET analysis revealed a specific surface area of 10.44&#xa0;m²g^-1, with a&#xa0;pore volume of 0.0042 cm³&#xa0;g⁻¹&#xa0;and&#xa0;an average pore size of 7.34&#xa0;nm for ZnO NPs. The photocatalytic capacity of the green synthesized ZnO nanoparticles was investigated against the photodegradation of Brilliant Cresyl Blue (BCB) dye while antimicrobial potential against <i>Escherichia coli</i> (<i>E. coli</i>), a gram-negative bacterium and <i>Bacillus subtilis</i> (<i>B. subtilis</i>), a gram-positive bacterium, and demonstrated good antimicrobial activity against both bacterial strains with a clear zone of microbial inhibition. 88.25% of BCB dye degradation at the optimized experimental conditions of dye concentration, photocatalyst dose, and pH(7.00) within 120&#xa0;min of visible light illumination was observed with a degradation rate of 0.0159&#xa0;min⁻¹, and the ZnO nanoparticles retained ~ 80% photodegradation efficiency after the fourth cycle of reuse. Moreover, the scavenger study results confirmed that the hydroxyl radicals were the key active species participated in the degradation of BCB dye. Therefore, the reported ZnO nanoparticles are potentially excellent photocatalysts as well as antimicrobial agents which can be effectively utilized for the&#xa0;environmental remediation purposes.</p> Graphical Abstract <p></p>