Soil organic carbon (SOC) sequestration in croplands is a key strategy for addressing climate change and food security. The effect of legume-inclusion diversified cropping systems (LICS) on global SOC sequestration remains unclear. This study conducted a global meta-analysis to quantitatively evaluate the impact of LICS on SOC content in croplands. Results showed that LICS significantly increased SOC content by 5.48% compared to systems without legumes. Subgroup meta-analyses identified key factors affecting SOC sequestration under LICS, with the greatest benefits observed in tropical and semi-arid climates and in loamy soils. Positive SOC responses to LICS were stronger with higher mean annual temperature, initial SOC and soil pH, but decreased with higher initial soil bulk density. SOC increases were more pronounced when the previous cropping system was continuous monoculture. Importantly, the positive effects of LICS on SOC were consistent across different farm management practices and regardless of legume crop functions. A global map of SOC responses to LICS was simulated, indicating that applying LICS in suitable regions could increase cropland SOC content by 5.60% and SOC storage by 2.94 t CO2 per hectare annually. Overall, this study highlights the strong global potential of LICS to enhance SOC sequestration in croplands and provides a high-resolution map to support the targeted implementation of legume-inclusion diversified cropping strategies worldwide.