Hexagonal boron nitride (hBN) with defects shows remarkable performance as catalyst support for single-atom stabilization in several catalytic reactions, such as CO oxidation, N₂ fixation, and ORR. However, the anchoring sites for single-atoms and their catalytic performance towards acetylene hydrochlorination still needs a comprehensive investigation. The boron and nitrogen-vacancy in hBN not only stabilizes Au but can also effectively tune its electronic structure. The single-atom Au has charged negatively and positively on hBN with the formation nitrogen (hBNv) and boron (hBvN) vacancy, respectively. The electronic structure analysis, MD simulations, phonon band structure, and migration barrier uncovered the stability of Au supported on hBN. The reaction proceeded either with Eley–Rideal (E-R) mechanism, starting with C₂H₂ adsorption after that HCl activation, product formation, or with Langmuir–Hinshelwood (L-H) method, starting with co-adsorption of C₂H₂ and HCl. The L-H mechanism results in a smaller reaction barrier of 0.90 and 1.15 eV compared to the counterpart E-R mechanism with a barrier of 1.14 and 1.25 eV for Au/hBNv and Au/hBvN respectively. Moreover, both Au in cation and anion state can efficiently catalyze acetylene hydrochlorination with a competing energy barrier. Overall, current research gives a comprehensive explanation of the catalytic properties of hBN-based single-atom Au catalyst.