Despite the well-established defect tolerance of metal halide perovskites (MHPs), there are multiple sources of defects in MHPs, such as grain boundaries in thin films, colloidal nanocrystal surfaces, and a heterointerface formed with the charge-transport layer, all of which play a crucial role in determining the efficiency and stability of light-emitting diodes (LEDs). Defect passivation strategies have become essential tools for improving device performance. Here, we analyzed and correlated the origins of the defects in MHPs to their influence on the optical and charge-carrier transport properties and systematically reviewed mechanistic principles of promising passivation strategies to either eliminate or suppress various defects that undermine the potential of perovskite LEDs. Several challenges and prospects for the future development of MHP LEDs have been identified. This review could provide a valuable reference for the community to promote the optimization and stabilization for developing high-performance MHP LEDs and further uncover the potential of MHPs for optoelectronic devices.