In this study, NiFe₂O₄/ZnO composites were biosynthesized using Muntingia calabura L. leaf extract and evaluated for Congo red dye photodegradation and antibacterial application. The material was characterized by X-Ray Diffraction (XRD), Scanning Electron Microscope-Energy Dispersive X-Ray (SEM-EDX), Ultraviolet–Visible Diffuse Reflectance Spectroscopy (UV-DRS), and Vibrating Sample Magnetometry (VSM) analysis, confirming successful synthesis. Optimization process was performed using Response Surface Methodology (RSM) with three variables: solution pH (4–10), dye concentration (10–40 mg/L), and irradiation time (30–90 minutes). The composite possessed a band gap energy of 2.23 eV along with magnetic characteristics, displaying a saturation magnetization of 42.89 emu/g. The crystallite size of the NiFe₂O₄/ZnO composite was determined to be 22.5 nm, confirming that this composite is on the nanoscale. The quadratic model (R² = 0.9890, p < 0.05) accurately described the degradation process, with optimum conditions at pH 6.20, dye concentration 38.10 mg/L, and irradiation time 52.30 minutes, achieving 98.10% degradation efficiency. A desirability value of 1 confirmed model validity, the predicted condition achieves the best outcome for all targeted responses simultaneously. The catalyst maintained stability during recycling, and antibacterial evaluation confirmed its effectiveness against Staphylococcus aureus and Escherichia coli. These findings highlight NiFe₂O₄/ZnO biosynthesized via Muntingia calabura L extract as an eco-friendly material with potential applications in wastewater treatment.