We report a comprehensive, multi-technique study of bismuth oxide growth on Au(111) under different conditions such as temperature and exposure to molecular oxygen. By combining synchrotron-based X-ray photoelectron spectroscopy and diffraction with low-energy electron diffraction and scanning tunneling microscopy, we elucidate the structural evolution of the system during controlled oxidation and subsequent annealing. We find that Bi deposition induces well-defined surface reconstructions, whereas oxidation triggers the formation of a complex sequence of bismuth oxide domains. High-resolution spectroscopic and diffraction data enable us to identify an oxide structure consistent with the $(201)$ surface of $\beta$-Bi${}_2$O${}_3$. In addition, angle resolved photoemission experiments and work function measurements reveal substantial electronic modifications triggered by a complex interplay of segregation of Bi and Au. Notably, a work function of 3.4~eV is achieved for oxidation at 423~K. These results provide benchmark structural and electronic insights into the Bi oxide/Au(111) system and establish a framework for integrating Bi${}_2$O${}_3$ as a contact material in devices using two-dimensional semiconductors, where it can enable low contact resistance.