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This study introduces an innovative plasmon-mediated strategy for the surface functionalization of colloidal gold nanoparticles (AuNPs) through the reductive grafting of calix[4]arene-based tetra-diazonium salts under pulsed laser irradiation. By exploiting the localized surface plasmon resonance (LSPR) of AuNPs, the diazonium salts were efficiently grafted onto the nanoparticle surface without the use of external reducing agents or photocatalysts. Optimization of experimental parameters, such as irradiation wavelength, power, and reaction time, enabled rapid and robust functionalization while minimizing nanoparticle degradation. Mechanistic studies confirmed that both hot electron generation and localized photothermal effects contribute to the grafting process, while surface analyses confirmed a denser calix[4]arene coating for the particles obtained by photografting. The method was successfully extended to other diazonium salts, with calix[4]arene derivatives yielding densely packed, highly stable organic shells. Compared to conventional chemical reduction, this laser-assisted approach significantly reduces reaction time and reagent consumption. Overall, the method provides a fast, efficient, and versatile strategy for the covalent functionalization of plasmonic nanoparticles in suspension.