The fields of information technology, energy, environmental science, medicine, homeland security, food safety, and transportation are impacted by nanotechnology, as they are based on developments in chemistry, physics, materials science, and biotechnology. Nanotechnology concerns materials with particles of a certain geometry ranging in size from 1-100 nm, thus exhibiting novel physical, chemical, and biological properties. Particles on these scales show markedly different properties to their bulk material counterparts. Green synthesis has continued to draw a significant interest in the context of materials science owing to its properties as an environmentally sustainable and eco-friendly approach in the synthesis of a variety of nanomaterials, including metal/metal oxide nanoparticles, hybrid materials, and bioinspired materials. This present study was undertaken to investigate the synthesis, characterization, and antioxidative and antibacterial activities of MnO, ZnO, and FeO NPs from tomato processing waste. Visual inspection, UV–visible spectroscopy, Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) were utilized for the characterization of the synthesized nanoparticles. Quantitative analysis focused on the presence of phenolic and flavonoid components in the nanoparticles. The total phenolic content was determined to be 22.098 ± 0.00153 mg GAE/g for MnO, 21.957 ± 0.0011 mg GAE/g for ZnO, and 21.100 ± 0.0005 mg GAE/g for FeO. The in vitro radical scavenging abilities of the nanoparticles were assessed using the DPPH assay, revealing IC50 values of 47% for MnO, 34% for ZnO, and 40% for FeO. Additionally, the antibacterial activities of the nanoparticles were tested against Escherichia coli (Gram-negative bacteria), Staphylococcus aureus (Gram-positive bacteria), and Escherichia faecalis (Gram-positive bacteria). The results underscore the potential of tomato waste-derived nanoparticles in antioxidant and antibacterial applications, highlighting their utility in the biotechnological and pharmaceutical industries.