In this study, we investigated the biogenic synthesis of nanostructured CuO and CuO/NiO nanocomposites using Azardica indica leaf extract as a reducing agent. The structure, surface morphology, and elemental compositions of the synthesized samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy with energy-dispersive X-ray (EDX) analysis, transmission electron microscopy, X-ray photoelectron spectroscopy (XPS), and Fourier transform-infrared spectroscopy. XRD analysis indicated that the CuO sample had a monoclinic structure and the CuO/NiO samples exhibited a phase mixture with monoclinic and cubic structures. The oxidation states and chemical compositions were identified based on the XPS and EDX spectra. Morphological observations showed that the synthesized samples had nanofiower and nanoflalce-like structures. The optical, magnetic, and thermal characteristics were determined using ultraviolet visible spectroscopy, photoluminescence, vibrating sample magnetometry, and thermogravimetry-differential scanning calorimetry. The dielectric properties of the semiconductor metal oxide nanocomposite structures matched well with the Maxwell-Wagner model, thereby indicating that the conducting grains were layered with poorly conducting grain boundaries. Higher dielectric constant values were observed for the CuO/NiO (salt molar ratio = 3:1) sample compared with the other compositions, which was attributed to the greater occupation of Cu2+ ions on the grain boundaries than the NI2+ ion. The green synthesized materials effectively degraded two hazardous water pollutants comprising methylene blue and eosin yellow.