Crystal violet (CV), a widely used dye in paints and textiles, poses a significant environmental threat due to its non-biodegradable nature. A modified slag-based geopolymer has been developed to address this issue by incorporating raw moringa seed powder (MSP), an agricultural waste. The geopolymers (SM1, SM2, and SM3) were created by adding different percentages of MSP (0.2%, 0.6%, and 1% by weight) to ground granulated blast furnace slag (GGBFS), using sodium silicate and 10 M sodium hydroxide as alkali activators. This combination enhances the geopolymer's mechanical and adsorbent properties, making it more effective for CV removal. The geopolymer composites were analyzed using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). Their mechanical properties were evaluated by conducting compressive strength and total porosity tests. Pore structure analysis was performed using nitrogen adsorption and desorption techniques, and the point of zero charges was determined. Additionally, batch experiments were carried out to investigate the adsorption of CV dye, employing two isotherm models and kinetic models for analysis. The SM1 mix, which is a modified slag-based geopolymer containing 0.2% MSP, exhibited the highest compressive strength at 73 MPa after 180 days, representing a 25.8% improvement compared to the control mix (100% slag). Furthermore, modified geopolymer mixes showed greater adsorption activity toward crystal violet compared to the control mix, with the SM3 mix achieving an adsorption capacity of up to 322.58 mg/g. The study demonstrates that adding MSP to slag-based geopolymer enhances mechanical strength and adsorption capacity. This indicates a positive impact on the composite's surface properties and highlights the environmental benefits of utilizing industrial and agricultural waste in wastewater treatment.