This study examines the use of jackfruit peels as a cost-effective precursor for creating activated carbon for carbon dioxide (CO2) capture. Hydrothermal carbonization was utilized to convert the peels into hydrochar, which was then activated with potassium hydroxide (KOH) at various ratios (1:1–1:3). The effects of these ratios on the physical and chemical properties of the activated carbon were analyzed using techniques like SEM, BET, and BJH. The results showed that chemical modifications effectively enhanced the surface area, porosity, and surface chemistry of the hydrochar, improving CO2 capture capabilities. The activated carbon with the highest KOH ratio had the greatest surface area and pore volume, demonstrating significant potential for CO2 capture. Specifically, the KOH-activated hydrochar with a 1:3 ratio and activated at 600 °C for 1 h had the highest CO2 adsorption capacity (69.79 mg/g), an 87% improvement over unactivated hydrochar. This study highlights jackfruit peels as a sustainable source for CO2-capturing activated carbon.