Leguminous cover crops (LCCs) are widely used as green manure in newly established and replanted oil palm plantations, offering benefits such as improved soil fertility, erosion control, weed suppression, and potential carbon sequestration. Their role is especially important in environmentally sensitive areas like tropical peat soils. This study estimated carbon stocks in oil palm ecosystems under different ground cover treatments on peat soil in Perak, Malaysia. A non-destructive method was applied to estimate carbon in oil palm biomass (above- and belowground), while quadrat sampling was used for LCCs biomass and soil coring for peat carbon assessment. The conventional LCCs mixture (Centrosema pubescens, Pueraria javanica, and Calopogonium sp.) recorded the highest total carbon stock at 15.89 Mg C ha^-1, while Mucuna bracteata had the highest ground cover carbon at 1.25 Mg C ha–1. Peat soil was the dominant carbon pool, contributing 91.54% of the total, followed by oil palm biomass (7.92%) and LCCs (0.53%). These findings suggest that planters can strategically select LCCs based on management objectives: mixtures for maximising overall carbon sequestration and M. bracteata for rapid soil surface protection. LCCs offer a dual benefit by supporting soil health while helping mitigate greenhouse gas emissions in peat-based agroecosystems.