Biomass-derived porous carbons have been considered as the most potential candidate for effective CO₂ adsorbent thanks to being widely-available precursor and having highly porous structure and stable chemical/physical features. However, the biomass-derived porous carbons still suffer from the poor optimization process in terms of the synthesis conditions. Herein, we have successfully fabricated coconut shell-derived porous carbon by a simple one-step synthesis process. The as-prepared carbon exhibits advanced textual activity together with well-designed micropore morphology and possesses oxygen-containing functional groups (reached 18.81 wt %) within the carbon matrix. Depending on the different activating temperatures (from 700 to 800 °C) and KOH/biomass mass ratios (from 0.3 to 1), the 750 °C and 0.5 mass ratio were found to be enabling the highest CO₂ capture performance. The optimal adsorbent was achieved a high CO₂ uptake capacity of 5.92 and 4.15 mmol·g⁻¹ at 0 and 25 °C (1 bar), respectively. More importantly, as-prepared carbon adsorbent exhibited moderate isosteric heat of adsorption and high CO₂/N₂ selectivity. The results were revealed not only the textural feature but also the surface functional groups critically determine the CO₂ capture performance, indicating coconut shell-derived porous carbon has a considerable potential as a solid-state adsorbent for the CO₂ capture.