As a prevalent problematic soil in geotechnical engineering, organic-rich soil exhibits inferior engineering characteristics that necessitate stabilization treatment in practical applications. Among various soil improvement techniques, chemical stabilization using Portland cement (PC) has gained widespread adoption due to its operational convenience. However, conventional PC involves not only environmental burdens associated with resource- and energy-intensive production processes and carbon emissions but also substantial interference from organic matter (OM) during its hydration process, inhibiting the formation of cementitious bonds. To address these challenges, this study proposes an innovative green stabilization approach using reactive MgO carbonation technology. A comprehensive investigation was conducted to evaluate the physicochemical evolution, mechanical behavior, and microstructural characteristics of organic soils under varying OM contents and carbonation durations. Key findings revealed that unconfined compressive strength demonstrated a linear inverse relationship with OM content while exhibiting time-dependent enhancement during carbonation. Strength development correlated positively with mass gain and dry density but inversely with water content. Microanalytical results indicated OM-dependent phase transformations, showing decreased nesquehonite crystallization and increased dypingite/hydromagnesite formation with ascending OM content. Mechanism analysis suggested that OM content regulated carbonation product speciation and aggregate morphology, thereby governing the coupled processes of particle cementation, pore structure refinement, and mechanical strengthening. This research demonstrates the technical viability of MgO carbonation for organic soil stabilization while contributing to sustainable geotechnical practices through carbon sequestration.