Given the substantial emissions of CO₂ into the atmosphere, there is a critical need for effective CO₂ adsorbents at scale, ideally derived from abundant and sustainable natural resources. In this work, microcrystalline cellulose derived from cotton is used to fabricate cellulose aerogel as porous support via a NaOH/urea-based dissolution and regeneration process, followed by surface modification with a series of amino silane coupling agents to produce aminated cellulose aerogel as CO₂ adsorbent. The as-synthesized optimal adsorbent exhibits a high CO₂ sorption capacity of up to 1.5 and 1.3 mmol g⁻¹ at 0 °C and 25 °C at 1 bar, respectively. Notably, in-depth analysis shows that the adsorbent achieves an impressive capacity of CO₂ uptake of 0.29 mmol g⁻¹ at 25 °C at an exceptionally low CO₂ pressure of 0.4 mbar, i.e., under ambient CO₂ pressure. It implies its potential use as adsorbent both for the traditional point-source capture and the direct air capture as an emerging negative emission technology. This study underscores the environmentally friendly, cost-effective, and biosourced attributes of aminated cellulose aerogel as a compelling alternative for carbon capture, contributing to global initiatives combating CO₂ emissions and stressing the key role of sustainable materials in tackling this global environmental challenge.