Abstract The current study reports on biosynthesisof pure graphitic carbon nitride (GCN), ZnO nanoparticles (NPs) and ZnO-doped gaphitic carbon nitridenanohybrids (ZnO/GCN-NHs) usingOcimumtenuiflorum(OT)leafextract.GCN synthesis using plant extract was never reported in previous studies. Under direct solar lightphotocatalytic performance of the synthesized GCN, NPs and NHs was tested on the degradation of methylene orange (MO) dye and compared. Among the samples, the ZnO/GCN-NHsexhibits superior photocatalytic activity, achieving up to 47.56% degradation in 150 min of MO dye. The cytotoxicity of the biosynthesized NPs and NHswas assessed against human dental pulp stem cells and these were found to be non-toxic, indicating their potential for biomedical applications. The antimicrobial properties were also assessed using well diffusion and disc diffusion tests against four bacterial strains i.e., two Gram-negative and two Gram-positive. The tests demonstrate significant antibacterial activity with a remarkable inhibition radius against Escherichia coli 17.5 ± 1mm, Pseudomonas aeruginosa 15.04 ± 1mm, Staphylococcus aureus 27.5 ± 1mm, and Streptococcus dysgalactiae 25 ± 1 mm. The enhanced photocatalytic and antimicrobial properties of the ZnO/GCN-NHs are hypothesized to be due to the increased production of reactive oxygen species (ROS) through the combination of ZnO NPs with biosynthesized GCN.