A novel gold–graphitic carbon nitride–polyaniline (Au@g-C₃N₄–PANI) nanoblend was synthesized via in situ oxidative polymerization of aniline using auric acid as an oxidant in the presence of g-C₃N₄. The structure and morphology of the nanoblend was characterized by UV-Vis, FT-IR, XRD, Raman, TGA, HR-TEM and SEM mapping analysis and the results demonstrate that Au nanoparticles with an average size of 10 nm are well-dispersed on the surface of g-C₃N₄–PANI. A systematic investigation of this new star Au@g-C₃N₄–PANI nanohybrid material shows an excellent catalytic performance in the hydrogenation of benzaldehyde (BZ) to benzyl alcohol (BA) in aqueous solution. The sustainable catalyst Au@g-C₃N₄–PANI has relatively high catalytic activity, stability and reusability compared to the sole and binary components, g-C₃N₄ and g-C₃N₄–PANI, under similar conditions. Au@g-C₃N₄–PANI exhibits a remarkable conversion percentage (99.9%), rate constant (0.5034 min⁻¹) and turnover frequency (0.1666 mM mg⁻¹ min⁻¹) for the reduction of BZ. Its enhanced catalytic activity is attributed to a strong synergistic effect arising due to inter-constituent interactions between the Au nanoparticles and the covalently grafted PANI on the g-C₃N₄. The rate of BZ hydrogenation is found to be dependent on the concentrations of catalyst, substrate and reductant and the type of solvents. The stability and reusability of the catalyst and the catalysis mechanism are investigated and discussed.