This study develops a graphical decision-making tool inspired by the break-even concept. It facilitates the selection of biomass utilisation where the highest possible profit and lowest GHG emissions indicate the optimal choice. The GHG intensity (kg CO2eq/MWh) and GHG price (USD/kg CO2eq) comprise the y-axis and x-axis of the Break-even Based Decision Making (BBDM) tool. The applicability of the tool is demonstrated by a case study where the biomass (switchgrass and wheat straw) is treated with slow pyrolysis for energy generation and/or biochar production. Burning for electricity is generally a preferable option, especially for countries with high GHG intensity. Biochar application as a form of carbon sequestration is suggested at low GHG intensity. This application becomes the preferred option when the GHG price is higher than 0.03 USD/kg CO2eq for switchgrass and higher than 0.01 USD/kg CO2eq for wheat straw. Wheat straw, as agricultural waste, has the advantage of lower GHG footprint while switchgrass offers a higher energy output. In general, the choice of the best use of biomass can be different under different circumstances. The developed tool is able to provide a rigorous basis for decision support when the GHG intensity and GHG price are defined.