L-Glutamic acid/ZnS (L-GA/ZnS) composites were prepared by varying the amount of ZnS addition ranging from 1–5 wt% by means of an easy solvent casting approach. The morphological investigation, antimicrobial activity, photocatalytic enactment, and electrochemical properties of the composites were evaluated. The formation of L-GA/ZnS composites was confirmed by FTIR, UV-Vis, and photoluminescence (PL) spectroscopy. Besides, FTIR, UV-Visible, and PL data revealed the possible incorporation of ZnS into L-GA. The L-GA/ZnS composites demonstrated similar plate-like structure of L-GA with agglomerated ZnS morphology on the plate surface with diameter in the range of 50–500 nm, confirmed by FESEM/EDS measurements. The prepared composites showed excellent photocatalytic depiction towards methylene blue (MB) degradation in comparison to L-GA and ZnS. A set of supercapacitor devices were fabricated using L-GA/ZnS composites. The performance of the supercapacitor was assessed by GCD and exhibited good energy storage capacity. The prepared composites showed promising prospects for hybrid supercapacitor application. These outcomes may offer new insight into the fabrication of L-GA/ZnS composites as photocatalysts for organic contaminants treatment.