In this study, a Mn-ZnO composite inorganic photocatalytic material with high antimicrobial properties was successfully synthesised using a facile hydrothermal synthesis method. The material was characterised by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectra and ultraviolet-visible diffuse reflection spectra, which confirmed the successful preparation of the material and showed that the introduction of Mn improved the separation efficiency of electron-hole pairs. In order to determine the optimum molar ratio of composites selected for subsequent experiments, this experiment was carried out by comparing the photocatalytic efficiencies of Mn-ZnO composite photocatalytic materials with doping molar ratios of 1%, 3% and 5%. The results demonstrated that the photocatalytic antimicrobial performance of the composites against bacteria was significantly higher than that of single ZnO nanomaterials at 1% Mn doping. In subsequent studies, a 35 W LED light was employed as the excitation light source, and the gradient dilution method and plate colony counting method were used to evaluate the photocatalytic antimicrobial performance of Mn-ZnO composite photocatalytic materials at different concentration gradients (125 mg/L, 250 mg/L, 375 mg/L, 500 mg/L, 1000 mg/L) against three bacterial species, namely, E. coli, S. aureus and Bacillus subtilis. In comparison to the pure ZnO control group, the composites demonstrated antimicrobial effects of 98.33%, 100% and 100% respectively, in a shorter period of time under light conditions with only 125 mg/L. These results indicate that the Mn-ZnO composite photocatalytic materials were more effective against E. coli, S. aureus and Bacillus subtilis than the pure ZnO. This suggests that the Mn-ZnO composite photocatalytic material exhibits high efficiency and broad-spectrum antimicrobial properties, capable of rapidly destroying a multitude of pathogenic microorganisms at a low concentration. Furthermore, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) experiments demonstrated that this highly antimicrobial composite photocatalytic material, which was synthesised by our research group, has good biocompatibility at the experimental concentration. Therefore, this study provides a cheap, environmentally friendly and facile method to prepare photocatalytic materials with high antimicrobial properties. This new class of functional materials may be used in the field of wastewater treatment in the future and has a promising future in practical antimicrobial applications.