Electrochromic materials can tune the illumination and heat exchange of a building with the environment and thereby save energy in lighting, heating, and air conditioning in a cost-effective way, which is vital in realizing carbon neutrality. 2D frameworks such as coordination nanosheets (CONASHs) that are widely explored for a wide range of applications in energy storage and conversion can be a cluster of novel electrochromic materials. In this work, a series of transition metal benzenehexathiol (TM-BHT) CONASHs are theoretically investigated via first-principles simulations. During ion intercalation and deintercalation in TM-BHTs, changes in lattice structures, lithium diffusion barriers, atomic charges, bond strength, and electronic properties are explored in-depth. The incurred changes are then correlated with critical electrochromic properties, including the transmittance adjustment ranges in the visible light, near-infrared, solar spectrum, and mid-infrared. Among the various TM-BHT systems, Cu-BHT and Ag-BHT are the most promising broadband electrochromic materials for optical and thermal management in the wavelength range from visible to mid-infrared. The theoretical guidance from this work paves a new path toward electrochromic applications of CONASHs that exploit the versatility of these 2D materials.