MXenes have shown significant potential in a multitude of scientific domains as they provide substantial benefits over carbon graphene, such as ease of production and functionalization, large surface area, adjustable properties, biocompatibility and hydrophilicity. The morphologies and physicochemical properties of MXenes vary with the synthesis procedures and conditions. Very recently, unique hybrid MXene-based nanocomposites have been produced and applied in a variety of fields. Herein, we review the synthesis of MXenes from traditional chemical exfoliation methods to newly developing fluoride-independent hydrothermal methods, summarize the properties of the synthesized MXenes, including stability and oxidative sensitivity, and outline emerging approaches for MXene-based nanocomposites. We also elaborate the up-to-date bio-applications of MXenes in photothermal therapy, bio-imaging, sensing, and drug delivery, as well as the practical hurdles that must be addressed.