Advanced materials such as transition-metal borides and their resulting 2D nanostructures play a pivotal role in surmounting barriers within energy storage and conversion technologies. This review article offers a unique and comprehensive exploration of MxBy and their derived 2D nanostructures, with a particular focus on their synthesis, properties, and applications across various energy storage and conversion technologies. The review begins with an in-depth analysis of the synthesis methods, stacking configurations, and physical characteristics of MxByderived 2D nanostructures, offering insights into their formation and structural properties. Specifically tailored to supercapacitor applications, the review examines the performance, charge storage mechanisms, and electrochemical efficiency of these nanostructures within this realm. Recent advancements in the field are highlighted, ensuring that the presented information is current and reflective of the latest findings and insights. The review also discusses the applications of transition-metal diborides in other energy storage and conversion technologies, including Li-ion batteries, Na-ion batteries and electrochemical reactions such as the OER, N2RR, HER, and CO2RR. Additionally, significant emphasis is placed on electrode architecture design and electrolyte composition, elucidating how these factors influence the overall performance of supercapacitors utilizing MxByderived 2D nanostructures. By integrating these components, the review provides valuable insights and updates to the existing body of knowledge in the domain of MxBy-derived 2D nanostructures-based electrochemical energy storage devices.