The increasing reliance on commercial inorganic fertilizers has raised significant environmental and economic concerns, including soil degradation, nutrient leaching, water pollution, and greenhouse gas emissions. This review critically evaluates biomass-derived chars produced via thermochemical processes, i.e., pyrolysis, gasification, and hydrothermal carbonization, as potential alternatives to synthetic fertilizers. Among the three biomass-derived chars, biochar stands out as the most viable option for soil amendment due to its high stability, nutrient retention capacity, and long-term carbon sequestration benefits. Gasification char, despite its high porosity and adsorption capacity, often lacks bioavailable nutrients, whereas hydrochar, though rich in organic compounds, poses challenges related to stability and phytotoxicity. Biochar application has been shown to significantly reduce N₂O emissions, enhance soil water retention, and mitigate nutrient runoff, offering clear environmental advantages over conventional fertilizers. Moreover, biochar has transitioned from an experimental soil amendment to a commercially available product with increasing adoption in agriculture worldwide, further reinforcing its practical viability. However, large-scale implementation still faces economic and logistical constraints, including high production costs, transportation inefficiencies, and regulatory uncertainties. Addressing these challenges through policy incentives such as subsidies and carbon credits can enhance the economic feasibility of biochar production and application. Given these findings, this review focuses on biochar as the most practical and sustainable alternative to commercial inorganic fertilizers.