Biochar application has emerged as a promising strategy for simultaneously improving soil fertility and mitigating climate change through carbon sequestration in agricultural systems. This study investigated the effects of biochar amendment at varying application rates (0, 5, 10, and 20 t ha⁻¹) on soil physicochemical properties, crop productivity, and greenhouse gas (GHG) emissions across three consecutive cropping seasons in tropical smallholder farms in subSaharan Africa. A randomized complete block design (RCBD) with four replications was employed across three agroecological zones with contrasting soil types. Results demonstrated that biochar application at 10 t ha⁻¹ significantly increased soil organic carbon (SOC) by 47.3%, cation exchange capacity (CEC) by 34.8%, and water retention capacity by 28.6% compared to unamended control plots. Maize grain yield increased by up to 62% under combined biochar and reduced nitrogen fertilizer application, suggesting potential for fertilizer use efficiency improvement. Greenhouse gas flux measurements revealed significant reductions in N₂O emissions (−38.4%) and CH₄ emissions (−22.1%) from biochar-amended soils. Economic analysis indicated a favorable benefit-cost ratio of 2.3:1 for biochar application when agricultural residue-derived biochar was produced locally. These findings suggest that biochar integration into smallholder farming systems represents a viable climate-smart agriculture strategy with co-benefits for food security and environmental sustainability.