Despite their impressive plasmonic photocatalytic activity, nanosized silver and silver halides always suffer from serious agglomeration and photocorrosion, thus are severely restricted in the practical wastewater restoration applications. The design and realization of plasmonic heterojunction nanostructures is an effective way to solve this stability problem, yet the ideal plasmonic catalyst dispersion and immobilization remains a great challenge. In this work, a highly immobilized Ag@AgCl/g-C₃N₄ plasmonic photocatalyst was developed through a rational in-situ implanting approach, in which the Ag can be homodispersely distributed and strongly coupled with prefixed Cl sites on g-C₃N₄ nanosheets (CNNS). The X-ray diffraction (XRD) pattern, X-ray photoelectron spectroscopy (XPS) spectra and element mapping images clearly proved the homodispersely distribution of nanosized Ag@AgCl on the CNNS. The optimal Ag@AgCl-3/CNNS plasmonic photocatalyst with a narrow band gap of 2.45 eV and large specific surface area of 52.9 m²/g performs well in model pharmaceutical wastewater bleaching reactions under visible light. More importantly, the Ag@AgCl-3/CNNS show good stability compared with the conventional inhomogeneously coupled AgCl/g-C₃N₄ control as verified by their ultralow silver leakage rate in water (0.00152 mg/g·d, accounts 6.9% that of the control) and a much lower corrosion current density (Icorr = 1.63 vs. 3.45 μA), recorded by Tafel slopes. The synergetic effect of surface plasmon resonance effect of nanosized Ag@AgCl with strong visible light harvesting ability and strong coupling between Ag@AgCl and exfoliated porous g-C₃N₄ nanosheets can support the fast separation of photogenerated electron–hole pairs, thus significantly improving the photocatalytic efficiency in the bleaching of antibiotic pollutants and bacteria. This work affords the great potential of the rational in-situ implanting design for high-performance and stable plasmonic photocatalysts.