Biochar is the carbon-rich soil amendment produced by the thermal decomposition (pyrolysis) of biomass. It attracted much interest because it contributes to sustainable soil fertility management and climate change mitigation. This paper reviews the potential impact of biochar on sustainable soil and crop productivity, carbon (C) sequestration and reduction of greenhouse gas (GHG) emissions. The unique characteristics of biochar, such as high surface area, surface charges, low bulk density, alkaline pH being recalcitrant to decomposition, high stability, and nutrient content are factors that enable it to sustainably improve soil and crop productivity and mitigate climate change. However, the pyrolysis technique, pyrolysis temperature and feedstock affect the characteristics and functions of biochar. Several studies have confirmed that biochar application improves soil properties such as soil porosity, structure and aggregation. It also enhances soil moisture holding capacity, pH, organic carbon (OC), CEC, total nitrogen (TN), available phosphorus (P), exchangeable potassium (K), and reduces phosphorus (P) fixation (immobilization). The above characteristics of biochar and volatile organic compounds provide a conducive habitat for microbes, enhance microbial population and enzymatic activities as well as nitrogen mineralization. They also help microbes to perform their functions, including decomposing organic matter, recycling nutrients, preserving soil structure, and releasing plant nutrients. However, biochar is more effective in sustainably improving crop production and contributing to food security and mitigating climate change when it is integrated with compost and manure application. Biochar provides a stable and inert form of C sequestration for long-term with a minimum risk of its return into the atmosphere. It also reduces GHG emissions through reducing nutrient losses, retaining, and cycling nutrients, and improving nutrient use efficiency. Though smallholder farmers in Sub-Saharan Africa (SSA) can produce biochar from unused crop residues and leftover fruits for home garden agriculture, this technology needs to be incorporated into soil management policy and transformed into large-scale schemes through using large feedstocks, including invasive species, municipality wastes and industry biproducts.