Two‐dimensional (2D) nanomaterials are attracting much attention due to their excellent electronic and optical properties. Here, we report the first experimental preparation of two free‐standing mercurated graphyne nanosheets via the interface‐assisted bottom‐up method, which integrates both the advantages of metal center and graphyne. The continuous large‐area nanosheets derived from the chemical growth show the layered molecular structural arrangement, controllable thickness and enhanced π‐conjugation, which result in their stable and outstanding broadband nonlinear saturable absorption (SA) properties (at both 532 and 1064 nm). The passively Q‐switched (PQS) performances of these two nanosheets as the saturable absorbers are comparable to or higher than those of the state‐of‐the‐art 2D nanomaterials (such as graphene, black phosphorus, MoS2, γ‐graphyne, etc.). Our results illustrate that the two metallated graphynes could act not only as a new class of 2D carbon‐rich materials, but also as inexpensive and easily available optoelectronic materials for device fabrication. Bottom‐up 2D metallated graphyne nanosheets exhibit their outstanding broadband nonlinear saturable absorption properties and can be used as excellent saturable absorbers in the passively Q‐switched Nd:YAG laser.