Thermogravimetric analysis of Persea americana seed powder (PASP) biomass was investigated at heating rates of 5, 10, 20, and 40 °C min−1 under an inert atmosphere to evaluate its thermo-chemical conversion behavior and pyrolysis kinetics. Two major mass-loss stages were observed between 300 and 1023 K, with the principal decomposition occurring between 450 and 600 K. The activation energies were determined using the Flynn–Wall–Ozawa (FWO), Kissinger–Akahira–Sunose (KAS), and Starink iso-conversional methods, yielding average values of 191.8, 202.7, and 202.2 kJ mol−1, respectively. The adsorption performance of PASP-biochar was evaluated for the simultaneous removal of Cd2+, Zn2+, Ni2+, Cu2+, Pb2+, Hg2+, and Co2+ from aqueous solution. The biochar exhibited good adsorption performance over a wide pH range, followed pseudo-second-order adsorption kinetics, and retained high removal efficiency after regeneration, indicating good reusability. Furthermore, preliminary techno-economic analysis confirmed that PASP-biochar can be produced economically, highlighting its practical potential as a sustainable adsorbent. Overall, this study demonstrates an integrated approach that combines thermo-chemical conversion, kinetic evaluation, and environmental application of avocado seed-derived biochar, providing an effective strategy for agro-waste valorization and sustainable heavymetal remediation from contaminated water.