<p>Quantum sensors have emerged as a promising tool in the field of fundamental biophotonics and advanced material science applications. The goal of understanding brain functions at the level of the individual neurons is a major concern of neuroscience. Nitrogen-vacancy (NV) centers in diamond offer a potential quantum sensing approach for recording very weak magnetic fields generated by neurons with remarkable spatial and temporal resolution. The review represents new developments in the use of NV-diamond magnetometry to brain mapping and bioimaging. The current significant advances include diamond nanopillar arrays, wide-field imaging, and NV-based detection of single-neuron signals. The NV magnetometry technique is superior in its ability to combine the spatial resolution of nanoscale with microseconds time resolution, which is better than conventional methods, such as functional magnetic resonance imaging (fMRI), electroencephalography (EEG), and magnetoencephalography (MEG). In the present article, we have discussed some of the issues, such as enhancing biocompatibility, minimizing noise, and combining NV sensors with other neurotechnology. This review provides a summary of the principles, current developments, and outlooks of NV-diamond magnetometry, which can greatly revolutionize the bioimaging and mapping of brain activity.</p>