<p>This study presents the synthesis and photocatalytic evaluation of indium (In), silver (Ag) and bimetallic indium-silver (In-Ag) nanoparticles supported on mesoporous carbon derived from the carbonization of giant cane waste. The photocatalysts were prepared via a hydrothermal route and comprehensively characterized by structural, morphological and surface analyses, confirming well-crystallized phases, uniform nanoparticle dispersion, and intimate contact between the metals and carbon matrix. Bimetallic integration induced notable electronic modulation, reducing the optical bandgap, enhancing visible-light absorption, and increasing the density of catalytically active sites. These synergistic effects facilitated efficient charge carrier separation and suppressed electron–hole recombination, leading to superior photocatalytic activity. Under visible-light irradiation, the InAgC nanocomposite achieved a methylene blue (MB) degradation efficiency of 95.43% within 120 min, significantly outperforming AgC (63.87%), InC (47.02%) and bare carbon (26.35%). Systematic studies of catalyst dosage and initial dye concentration further elucidated the structure–activity relationship, confirming the robustness of InAgC for wastewater treatment applications. This work underscores the promise of bimetallic-carbon hybrid architectures derived from sustainable biomass precursors as efficient and eco-friendly photocatalysts for the degradation of organic contaminants.</p>