Transition metal oxide (TMO)-decorated TiO₂ catalysts excel at low-temperature Hg⁰ oxidation. However, TMOs are typically found in large nanoparticles (NPs), resulting in a lower atom utilization efficiency. The current paper presents the design of an Au single atom (SA)-doped Ti⁴⁺ defected TiO₂ (Au SAC-Ti_1-xO₂) and investigations concerning the influence of an O-Au-O coordination environment on Hg⁰ oxidation. Au SAC-Ti_1-xO₂ was designed using an O-Au-O coordination environment and the O-Au-O orbital interaction was elucidated using density functional theory (DFT). The enhanced oxidative capability of lattice oxygen atoms and the interaction between Hg⁰ and oxygen atoms were investigated. The O-Au-O coordination environment containing Au SAC Ti_1-xO₂ was then synthesized and characterized using X-ray absorption fine structure (XAFS), X-ray photoelectron spectroscopy (XPS), etc. Finally, Hg⁰ oxidation catalytic activity was determined. Due to the increasing population of Au-O antibonding orbital interactions in the valence band, the bond order of O-Au-O in Au SAC Ti_1-xO₂ decreased significantly, thereby enhancing the oxidation ability of its adjacent oxygen atoms. Au SA and ultra-small Au clusters coexisted on a Ti_1-xO₂ catalyst, and the Hg⁰-oxidation efficiency at 150–200 °C was 14 times and 1.5 times greater than those of TiO₂ and 0.1 % Au/TiO₂, respectively. Furthermore, Au SAC Ti_1-xO₂ was more resistant to the inhibition of SO₂ and NO. It provides an efficient method for developing highly active SA catalysts for Hg⁰ oxidation.