<p>Synthetic organic dyes released from industries pose significant environmental and health hazards due to their toxicity, persistence, and resistance to conventional degradation processes. Traditional water treatment methods often suffer from limited efficiency, high energy requirements, and an inability to simultaneously remove both chemical and microbial contaminants. So, in this study, a solar light active ZnO/g-C₃N₄ nanocomposite was developed using a combination of sol–gel-combustion-impregnation methods, which showed an excellent water pollutant treatment and antibacterial efficiency. The catalytic activity of ZnO, g-C₃N₄, and ZnO/g-C₃N₄ nanocomposite was investigated by the degradation of aqueous solution of methylene blue (MB), rhodamine B (RhB), and malachite green (MG) dyes under direct sunlight irradiation. Further, the effect of operational parameters such as catalyst dosage, pH of dye solution, and initial dye concentration on the photocatalytic degradation efficiency were studied. The result revealed that ZnO/g-C₃N₄ (1:1.0) nanocomposite exhibited higher degradation efficiency towards dyes and the order of catalytic activity is ZnO/g-C₃N₄ (1:1.0) &gt; ZnO/g-C₃N₄ (1:1.5) &gt; ZnO/g-C₃N₄ (1:0.5) &gt; g-C₃N₄ &gt; ZnO, respectively. The 10&#xa0;mg/L initial dye concentration, 50&#xa0;mg catalyst dosage, and pH 9 are the optimized reaction parameters for highest photocatalytic activity with excellent reproducibility. The degradation was confirmed by kinetic analysis and proposed a possible mechanism for degradation. In addition, the catalytic active ZnO/g-C₃N₄ (1:1.0) nanocomposite displayed excellent antibacterial activity against gram-positive (<i>Staphylococcus aureus</i> and <i>Bacillus cereus</i>) and gram-negative (<i>Vibrio alginolyticus</i> and <i>Klebsiella pneumonia</i>) bacteria. The result concludes that ZnO/g-C₃N₄ nanocomposites are an efficient solar light-activated photocatalyst and excellent anti-bacterial agents under present experimental conditions.</p>