This study investigates the synthesis of highly porous ZnCl-activated biochars derived from sawdust through controlled pyrolysis at 300 °C and 500 °C, aiming to enhance CO adsorption performance. The effects of pyrolysis temperature and chemical activation on particle size distribution, surface area, and pore structure are systematically analyzed. Particle size analysis reveals that higher pyrolysis temperature and ZnCl activation significantly reduce both median and mean particle sizes, resulting in finer and more uniform biochar morphology. BET analysis demonstrates a substantial increase in specific surface area and micropore volume upon ZnCl activation, particularly at 500 °C, where the activated biochar (S500ZC) exhibits a high surface area of 717.60 m/g and a micropore area of 616.60 m/g. CO adsorption isotherms recorded at 25 °C confirm that both thermal treatment and activation markedly enhance adsorption capacity, with the highest uptake of 35.34 cm/g achieved by S500ZC. The adsorption performance follows the order: S300NZC < S300ZC < S500NZC < S500ZC, closely correlating with microporosity and surface textural development. The findings highlight the potential of ZnCl-activated biochars as cost-effective, environmentally friendly, and efficient sorbents for scalable CO mitigation technologies.