Marginal lands, representing approximately 1.5 billion hectares globally, present significant untapped potential for carbon sequestration through strategic agroforestry implementation. This study evaluated carbon sequestration potential across different agroforestry systems established on marginal lands including degraded agricultural areas, abandoned farmlands, and steep slopes in temperate and tropical regions. Over a 12-year monitoring period (2011-2023), we assessed above-ground and below-ground carbon stocks in silvopastoral systems, alley cropping, windbreaks, and riparian buffer systems compared to abandoned land controls. Results demonstrated substantial carbon accumulation rates ranging from 2.1 to 8.7 Mg C ha [−1] yr [−1], with silvopastoral systems achieving the highest sequestration rates (8.7±1.2 Mg C ha [−1] yr [−1]). Total carbon stocks after 12 years ranged from 89.3 Mg C ha [−1] in windbreak systems to 156.8 Mg C ha [−1] in mature silvopastoral systems. Soil organic carbon increased by 35-75% across all agroforestry treatments, with the greatest improvements observed in alley cropping systems (2.8±0.3 Mg C ha [−1] yr [−1]). Tree species selection significantly influenced carbon accumulation, with fast-growing nitrogen-fixing species achieving 40-60% higher sequestration rates than non-nitrogen fixing species. Economic analysis revealed net present values ranging from $1,250-3,800 ha [−1] over 20 years, indicating strong financial viability. These findings suggest that agroforestry systems on marginal lands could contribute 0.8-2.2 Pg C yr [−1] to global carbon sequestration, representing 8-22% of the carbon mitigation required to limit warming to 1.5 °C.