The pursuit of high-performance supercapacitors necessitates the development of advanced electrode materials with tailored structural and electrochemical properties. In this context, in-situ characterization techniques have emerged as pivotal tools for unveiling the dynamic processes that govern charge storage at the material electrolyte interface. This review presents a comprehensive overview of state-of-the-art in-situ techniques such as Raman spectroscopy, Fourier-transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM), and electrochemical liquid-phase TEM (LP-TEM) and highlights their applications in the real-time analysis of supercapacitor materials. These techniques provide critical insight into ion transport kinetics, phase transitions, redox reactions, and interfacial phenomena, all of which are vital for optimizing material performance. Emphasis is placed on how in-situ methods facilitate the rational design of MXenes, MOFs/COFs, hierarchical nanostructures, and flexible composites, leading to enhanced energy density, power output, and cycling stability. Special attention is also given to recent advancements in in-situ investigations of flexible and wearable supercapacitors. By correlating material behavior under operating conditions with device-level performance, this review outlines the current challenges and future opportunities in the integration of in-situ characterization into the accelerated development of next-generation energy storage systems.