Understanding the stability and catalytic behavior of atomically thin metal monolayers is crucial for the rational design of efficient electrocatalysts. This study employs an iterative DFT-AIMD-DFT multiscale simulation strategy to systematically uncover the structural evolution, electronic structures, and their correlations with catalytic performance in grouped transition metal monolayers (Au1L, Ag1L, Cu1L, Pt1L, Rh1L, Ir1L, Pd1L, and Ni1L). The results demonstrate that these monolayer metals exhibit a continuous transition from typical low-index facets to bilayer structures, with their stability strongly dependent on electronic structure and interlayer interactions. Key drivers of structural planarity and stability—spreading energy and interlayer interaction energy—were identified. Low coordination-induced electronic localization reveals the structure-electronic-performance coupling of metal monolayers under the synergistic regulation of work function and d-band center. Further analysis indicates that monolayer metals can maintain good stability over a wide electrochemical window, significantly enhancing their hydrogen oxidation reaction and oxygen reduction reaction catalytic activity, and exhibiting clear advantages over bulk metals. In particular, certain monolayer metals (e.g., Rh1L) achieve a synergistic optimization between stability and catalytic activity, fully demonstrating their tremendous application potential in the field of electrocatalysis.