Recently, graphitic carbon nitride nano-photocatalysts (GCN-NPCs) have been found to be a promising approach toward wastewater remediation. However, traditional physicochemical techniques have raised environmental concerns due to the use of toxic compounds and generation of dangerous by-products for surface modification and the reduction of metal ions. To overcome these issues, plant-mediated approach is considered an eco-friendly, easy, stable, and cost-effective means for the synthesis of GCN-NPCs. In this work, we focus on the biosynthesis of GCN-NPCs using Ocimum tenuiflorum plant leaves and their nanohybrids (NHs) combined with biosynthesized zinc oxide (ZnO/GCN-NHs) using the same plant extract. Their structural, chemical, and optical properties were further studied using UV-Vis spectroscopy; photoluminescence; X-ray diffraction; Fourier transform infrared spectroscopy; scanning electron microscopy; energy-dispersive X-ray spectroscopy and transmission electron microscopy. The photocatalytic properties of the successfully synthesized GCN, ZnO NPs, and ZnO/GCN-NHs were assessed towards methylene orange (MO) dye degradation. The antimicrobial properties of the same were studied against four different strains (Gram-negatives, Gram positives). ZnO/GCN-NHs demonstrated superior photocatalytic activity for degrading MO dye with a low band gap of 2.62 eV. Photocatalytic efficiency improved, showing a rate constant 3 times higher than pure GCN. Moreover, biosynthesized ZnO/GCN-NHs does not exhibit any cytotoxicity against bovine oviduct epithelial cells, which makes them suitable for biomedical applications. However, well diffusion, disc diffusion tests demonstrate significant antibacterial activity with remarkable inhibition (in radius) against Escherichia coli 17.5±1mm, Pseudomonas aeruginosa 15.04±1mm, Staphylococcus aureus 27.5±1mm, and Streptococcus dysgalactiae 25±1 mm. The main hypothesis of such enhancement of the photocatalytic and antimicrobial properties of the ZnO/GCN-NHs could be the production higher amount of were reactive oxygen species (ROS) that are well-knownto degrade organic compounds such as dyes, and kill bacteria. In ZnO compound, excited electron-hole pairs (excitation) are created under light excitation. These excitations react with hydroxyl and oxygen molecules, which induce ROS formation [1]. The anchoring of ZnO nanoparticles on the surface of GCN probably promotesthe formation of excitations through a better electron transfer that boost/assist ROS formation. This enhancement is presently attributed to the better separation of photogenerated charge carriers resulting from the development of a heterojunction among the interfaces of pure GCN and ZnO and must be further investigated. The high antimicrobial activity coupled with their lower cytotoxic effect highlights a potential therapeutic value that will be assessed.Ref. https://doi.org/10.3390/nano13131998.Ack: Mobilitas+PDF grant MOBJD1204 and ETAg Team Grant PRG2115.