Cadmium contamination in waters and soils can lead to food chain accumulation and ultimately human health degradation; means for reducing bioavailable Cd are desperately required, and biochars may play a role. Long-term lab incubation experiments were utilized to explain wheat straw-derived biochar (0, 5, and 15% by wt.) effects on Cd sorption and decreasing Cd bioavailability in soils and solutions, and to identify Cd forms present using both the European Community Bureau of Reference (BCR) chemical sequential extraction procedure and synchrotron-based X-ray absorption spectroscopy (XAS). Biochar Cd removal was up to ~90% from Cd-containing solutions and contaminated soil as compared to the control. Based on the wet chemical sequential extraction procedure in conjunction with XAS, biochar application promoted the formation of (oxy)hydroxide, carbonate, and organically bound Cd phases. As a material, biochar may be promoted as a tool for reducing and removing bioavailable Cd from contaminated waters and soils, potentially improving environmental and human health.