Fire safety has always been an important research topic in safety science. MXene nanosheets are considered one of the most promising flame retardants due to their unique physical structure and chemical properties. Chemical modification or synergistic use with other flame retardants can enhance their flame retardancy. Currently, there are various methods for preparing MXene nanosheets with advantages and disadvantages. This paper summarizes the research progress of MXene nanosheets in polyurethane, polylactic acid, polyimide, epoxy resin, cotton fabric, and wood, based on the fire-retardant mechanism. With the increasing demand for engineering applications, the multifunctionalization of MXene nanosheet-based composites will become a crucial development direction. These materials will play a significant role in safety protection across various fields, such as fire-retardant, thermal protection, electromagnetic shielding, and corrosion protection.