Discharge of dye-containing industrial effluents into water bodies poses a threat to the environment and public health due to the recalcitrant and toxic nature of synthetic dyes such as methylene blue (MB). In this study, a low-cost and environmentally friendly approach towards removal of MB from water systems was investigated using a new composite adsorbent. The adsorbent was synthesized by incorporating activated carbon—prepared from Bauhinia purpurea seedpods—into a polyurethane matrix. Batch adsorption experiments were conducted to examine the influence of most significant operating parameters, such as pH, contact time, initial dye concentration, and activated carbon loading, on the efficacy of removal of dye. Material characterization techniques such as Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), and X-ray Diffraction (XRD) were used to quantify morphology and functional groups, whereas X-ray Fluorescence (XRF) was used to quantify the elemental composition of the raw biomass. The results verified that optimum removal of dye (97% efficiency) was achieved using a 30% loading of activated carbon, initial dye concentration of 100 mg/L, unchanged pH, 25 °C temperature, and 240-minute contact time. Data for adsorption isotherms were best described using the Langmuir isotherm model, which points towards monolayer adsorption, whereas kinetic data fitted well with both pseudo-first-order and pseudo-second-order models. This research recognizes the potential of agro-waste composites as efficient and green adsorbents for wastewater treatment and dye decolorization in enhancing circular and sustainable water management.