Two-dimensional (2D) materials have emerged as a frontier in the research of next-generation optoelectronic and quantum devices due to their uniquely confined electronic structures and remarkable quantum effects. However, a significant portion of theoretically predicted 2D materials, particularly monoelemental 2D materials, such as silicene, germanene, and borophene, lack natural bulk layered counterparts and exist in thermodynamically metastable states, making them inaccessible via traditional mechanical exfoliation. This review systematically evaluates the "bottom-up" epitaxial growth of 2D materials on various metal substrates from an experimental perspective. We systematically discuss the multifaceted roles of metal substrates in governing growth mechanisms, including lattice-matching, step-edge guided unidirectional growth, and surface catalysis models (self-limiting and dissolution-precipitation). By modulating interfacial interactions and space-group symmetry, these substrates not only stabilize metastable phases but also enable the synthesis of wafer-scale single-crystal films. By integrating advanced characterization techniques such as scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), and angle-resolved photoemission spectroscopy (ARPES), we summarize the structural phases and electronic properties of diverse 2D systems, ranging from graphene on transition metals to novel binary compounds like PtTe₂ and MoS₂. Finally, we provide insights into the challenges of controllable large-scale synthesis and the integration of these materials into functional nanodevices. This work underscores the potential of metal-substrate-assisted growth in expanding the 2D material library and its far-reaching implications for energy storage, high-sensitivity sensing, and flexible nano-electronics.