Biochar produced from natural materials fixes carbon dioxide (CO2) from the atmosphere. Here it is investigated as a way to offset the CO2 emissions associated with cement-based stabilizers commonly used to solidify geomaterials for ground improvement. Three types of biochar made from different feedstocks (wood, bamboo, and rice husks) are added to a soil-cement slurry, and the effect of biochar type on the flowability and strength properties of the resulting soil cement is investigated in laboratory tests. Blast furnace cement type B is selected as the stabilizer in the tests. Based on an established methodology, the amount of CO2 fixed in the three types of biochar is calculated. Stabilizer is added at five levels: 40, 80, 120, 150, and 300 kg/m3. Biochar is added at amounts per cubic meter that offset or more than offset the CO2 emissions associated with the stabilizer. It is found that the flow value of the soil cement decreases with biochar addition. The original feedstock determines the rate of decrease, and there are two general trends of decrease. The unconfined compression strength of soil cement after 28 days of curing increases with the addition of biochar. It reaches a maximum when the amount of stabilizer added is 80 kg/m3, an addition rate still ensures workable flowability (a flow value of 110 mm or more), regardless of original feedstock.