The water-gas shift (WGS) reaction is a key process for hydrogen production, requiring efficient and stable catalysts. Bimetallic Cu–Au nanoparticles offer tunable catalytic properties through their alloy composition and structure arrangement, which affects adsorption and energy barriers. In this work, the catalytic activity of CuAu alloys in the WGS was investigated using multiple computational methods. Density functional theory (DFT) was used to investigate the surface stability and energetics of Cu, Cu₃Au, CuAu, and CuAu₃ alloys. Surface energies, calculated with PBE and PBE-D3, were used for the Wulff construction, where the (111) facet is highlighted as the dominant facet. Adsorption geometries of key intermediates were evaluated on (111) surfaces, and energy barriers were determined using ML-NEB. Both the direct (redox) and associative (COOH) pathways for WGS were evaluated, with the associative pathway preferred across all systems. Kinetic Monte Carlo (KMC) simulations at 300 and 400 °C over a defined range of partial pressures were used to link DFT-derived energetics to catalytic performance. The simulations predict turnover frequencies (TOF) that indicate the order of catalytic activity, with Cu > Cu3Au > CuAu > CuAu3. Surface coverages were low at higher temperatures, and rate-limiting steps for each mechanism varied depending on composition: O-H* cleavage or CO-O* formation for the direct pathway, and CO-OH* or COOH* for the associative pathway. In parallel, Ar⁺ ion-beam irradiation simulations were performed to evaluate its impact on the nanoparticles’ structure and to potentially infer effects on active-site distribution and catalytic performance before and after the ion beam. The results show how alloying modifies catalytic behavior and how irradiation can also be used, offering insights for the rational design of improved catalysts for the WGS reaction.