Density functional theory is employed to investigate the role of Au charge in the water-gas-shift (WGS) reaction on a CeO₂(111) surface with a cerium atom replaced by a gold atom. The oxidation state of the gold atom, varied between +3 and −1, is controlled by altering the number and configuration of oxygen vacancies. The findings indicate that Au³⁺ and Au⁻ are not catalytically active for the WGS reaction because of a high energy barrier of +1.54 eV required to dissociate water and +1.40 eV to produce H₂ and CO₂, respectively. However, when Au is in a modest oxidation state of +1, the overall reaction barrier for the WGS reaction via the carboxyl mechanism is reduced to 0.79–0.98 eV. It therefore appears that Au species with an oxidation state of +1 play a significant role in the WGS reaction at low temperatures (T < ∼550 K).