The application of phosphorescent heavy-metal complexes with d(6), d(8) and d(10) electron configurations for bioimaging is a new and promising research field and has been attracting increasing interest. In this critical review, we systematically evaluate the advantages of phosphorescent heavy-metal complexes as bioimaging probes, including their photophysical properties, cytotoxicity and cellular uptake mechanisms. The progress of research into the use of phosphorescent heavy-metal complexes for staining different compartments of cells, monitoring intracellular functional species, providing targeted bioimaging, two-photon bioimaging, small-animal bioimaging, multimodal bioimaging and time-resolved bioimaging is summarized. In addition, several possible future directions in this field are also discussed (133 references).