Polluted water sources are a growing concern in our world today, with more and more of our precious freshwater sources becoming contaminated. Pollution can come from a variety of sources, such as industrial discharge, agricultural runoff, and even urban runoff. Several treatment technologies have been investigated, mainly for dye pollution from textile and industrial wastes. In this study, the biosorption of methylene blue dye from the water environment was examined utilizing a low-cost and biodegradable biomaterial. Waste fish scales modified with NaOH were used as biomaterial. The biosorption effect of methylene blue concentration and pH variables was optimized. SEM for the surface morphology of the biomaterial and FT-IR analyses for the detection of functional groups were performed. The characterization of methylene blue biosorption was conducted to fully understand its nature, including its kinetics, equilibrium, and thermodynamic works. It has been determined that the biosorption process conforms most closely to the pseudo-second-order kinetic model for its kinetic results and to the Langmuir isotherm for its equilibrium results. Based on the Langmuir isotherm data, the maximum capacity for biosorption (qmax) was found to be 344.82 mg g−1. The thermodynamic results showed that the process of biosorption of methylene blue on various surfaces is spontaneous and occurs via physisorption. Additionally, the experimental design method was utilized to determine the optimum conditions of the methylene blue biosorption process under various conditions. The maximum biosorption capacity was determined to be 102.367 mg g−1 at the optimal conditions. The potential of biosorbent derived from the waste fish scales is promising as a novel biosorbent material due to its unique surface morphology and high biosorption capacity.