Developing a green, efficient, and robust route for fabricating silver nanoparticle (Ag-NP) composites remains a crucial challenge, particularly in achieving uniform particle size and high Ag-NP loading. In this study, a simple in-situ strategy was employed to synthesize and immobilize Ag-NPs (1–15 wt%) onto a bio-derived hydroxyapatite-curcumin (HAP-curcumin) nanocomposite. HAP was sustainably extracted from Black Tilapia fish scales, while curcumin functioned as both a natural reducing and stabilizing agent, enabling an environmentally friendly synthesis process. Structural and physicochemical analyses, XRD, FTIR, BET, XPS, and HRTEM, confirmed the successful formation and uniform dispersion of spherical Ag-NPs (∼15.7 nm) on the HAP-curcumin surface. The nanocomposites exhibited outstanding catalytic performance, efficiently reducing various organic pollutants, including 4-nitrophenol, Congo red, methylene blue, and rhodamine B, in the presence of NaBH₄. Remarkably, the 15% Ag/HAP-curcumin sample achieved rapid degradation of 4-nitrophenol within 5 s (k = 2.3297 min⁻¹) and demonstrated strong catalytic activity even in real sample matrices (milk, juice, and soap-containing wastewater). The 15% Ag/HAP-curcumin nanocomposite showed excellent stability over repeated cycles with negligible Ag leaching, indicating strong potential for practical applications. Beyond catalysis, the nanocomposites displayed potent antimicrobial activity against Bacillus cereus, Staphylococcus aureus, Staphylococcus hominis, and Candida albicans. The 15% Ag/HAP-curcumin nanocomposite achieved complete (100%) inhibition at 150 μg/mL, highlighting its dual functionality as a green catalyst and antimicrobial agent. This work presents a sustainable route for designing multifunctional Ag-based nanocomposites with promising applications in environmental remediation and biomedical fields.