Biochar (BC) is used for reductive dehalogenation and detoxification of chlorinated ethylenes, and its catalytic reactivity strongly depends on the type and composition of the biomass. This study aimed to alter the catalytic activity of biochar by using chemical amendments as an alternative to biomass feedstock screening. Three types of amendments including nonmetal elements (urea for N, sodium dodecyl sulfate for S), transition metal elements (MnSO₄ for Mn, FeSO₄ for Fe), and alkali/alkaline-earth metal elements (CaCl₂ for Ca, NaCl for Na) were added to biomass substrate (peanut shell) before pyrolysis at 950 °C to produce 6 different chemically amended BCs. Structure, functional groups, sorption and redox properties of the BCs were characterized, and the catalytic reactivity of the BCs for trichloroethylene (TCE) reduction with a layered iron (II, III) hydroxide (green rust) as reductant was tested. Amending BC with transition metals increased the specific surface area (SSA) of BC and in turn the adsorption affinity, while nonmetals and alkali/alkaline-earth metal amendments decreased SSA. The TCE dechlorination rate increased by 3.5 and 2.5 times for BCs amended with N and S, respectively, compared with Raw-BC, while amendments with Mn, Fe, Ca, and Na had minor effects on reactivity. A second-order kinetic model for TCE reduction was developed, pointing out the critical role of the BC reactive site concentration and competing adsorption of TCE to inreactive surfaces. A conceptual model is proposed for TCE reaction with reactive sites and inreactive adsorptive surfaces on BC. This study suggested demonstrates that the reactive sites density is critical for BC catalytic reactivity, and N amendment is most efficient for improving BC reactivity.