Due to its unique properties and advantageous traits, zinc oxide has garnered significant attention in recent years for the green synthesis of ZnO nanoparticles (ZnO-NP). This paper is focused on the synthesis of ZnO-NPs mediated by Adiantum capillus-veneris L. leaf extract and assesses their potential biological activities. In this study, ZnO-NP is synthesized using A. capillus-veneris L. leaf extract. The synthesized nanoparticles are characterized using, UV–vis spectroscopy, energy-dispersive X-ray spectroscopy (EDX), (SEM) scanning electron microscopy, X-ray diffraction (XRD), and Fourier transform infrared (FT-IR) spectrophotometry. The antibacterial, antifungal, anti-inflammatory, and antioxidant properties of the formulated ZnO-NPs are also inspected. The UV–vis, XRD, SEM, EDX, and FTIR confirmed the formation and purity of synthesized ZnO-NPs. The ZnO-NPs exhibit efficient antimicrobial potency against Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Aspergillus niger, and Aspergillus fumigatus. Gram-positive bacteria, particularly S. aureus, are more susceptible to ZnO-NPs, with the largest inhibition zone of 32 mm. In contrast, E. coli and P. aeruginosa display smaller inhibition zones of 25 and 27 mm respectively. Anti-inflammatory tests show that ZnO-NPs have a significant anti-inflammatory effect against egg albumin and bovine serum albumin denaturation, possess low toxicity on erythrocytes, and are highly hemocompatible.