<jats:p> In this research work, the Allium cepa (AC)bulb-based zinc oxide nanoparticles (ZnO-NPs) were prepared successfully through a green synthesis approach. Phytocompounds present in the Allium cepa bulb successfully reduced and stabilized the Zn<jats:sup>+2</jats:sup> ions into ZnO-NPs. Synthesis of the liquid form (L-ZnO-NPs) and calcined form (C-ZnO-NPs) were carried out. The color change of nanoparticles (NPs) colloidal solution from transparent to yellow, the surface plasmon resonance (SPR) peaks by UV-Visible spectroscopic analyses at 350 nm and 370 nm and Infrared spectrum shown functional groups below 700 nm, confirmed the synthesis of ZnO-NPs. The elemental composition of NPs revealed that the molecular weight of Zinc was 66 % and 61 % while Oxygen was 24 % and 26 % respectively in C-ZnO-NPs and L-ZnO-NPs. The scanning electron microscopy and X-ray diffraction pattern confirmed the successful synthesis of rod-shaped, crystalline ZnO-NPs (30-35 nm) with uniform distribution. The 2,2-Diphenyl-1-picrylhydrazyl (DPPH) assay-based antioxidant potential of C-ZnO-NPs and L-ZnO-NPs were recorded as 72 % and 65 % inhibition respectively while hydrogen peroxide (H<jats:sub>2</jats:sub>O<jats:sub>2</jats:sub>) radical scavenging assays revealed 62 % and 48 % inhibition respectively at 75 µL concentration. ZnO-NPs showed good antimicrobial, in-vitro anti-diabetic and antioxidant potential. Hence, Allium cepa bulb based ZnO-NPs through a green chemistry approach can be considered an innovative addition to the science of free radical scavenging, diabetes, and microbial infection management. </jats:p>