This study presents a multicriteria decision-making approach using the AHP-TOPSIS method to evaluate agricultural biomass for sustainable biochar production. Given the increasing demand for eco-friendly soil amendments, water treatment efficiency and renewable energy sources, identifying optimal agricultural biomass feedstocks is crucial. Key factors influencing biochar quality, including lignin content, carbon content, and nitrogen content, were prioritized during the selection process. A comprehensive evaluation was conducted, incorporating proximate analyses, Fourier Transform Infrared Spectroscopy (FTIR), and heating value assessments to verify the beneficial properties of various agricultural biomass types. After selecting the most suitable biomass of each kind, Thermogravimetric Analysis was employed to explore the thermal behaviour and biochar production potential of the selected materials. The results revealed that Fraxinus excelsior stood out with 18.16% lignin, 46.77% carbon, 0.52% nitrogen, 1.35% moisture content, and a calorific value of 20.24 MJ/kg, surpassing other samples. FTIR analysis confirmed the presence of functional groups in Fraxinus excelsior that enhances biochar stability. Furthermore, a combination of Fraxinus excelsior and Triticale demonstrated excellent thermal behaviour in Thermogravimetric Analysis, showing the highest residual mass at 760.5 °C (29.26%). These findings highlight that agricultural biomass not only offers favourable chemical and thermal properties but also contributes to sustainability by utilizing agricultural waste.