A shape-stabilised phase change material (SSPCM) was successfully synthesised using a microwave-assisted one-pot method, incorporating eicosane (EI) as the latent heat storage medium and expanded graphite (EG) as the supporting matrix. The process involved the microwave-induced expansion of EG in molten EI, promoting effective infiltration and encapsulation of the PCM. The resulting composites, prepared with EG concentrations ranging from 10 to 25 wt%, were thoroughly characterised to evaluate their thermal and structural properties. Differential scanning calorimetry (DSC) revealed that while the EG addition had minimal impact on the phase change temperatures, it led to a progressive decrease in latent heat with increasing EG content. Thermogravimetric analysis (TGA) indicated enhanced thermal stability of the composites due to the physical confinement of EI within the EG matrix. Fourier transform infrared spectroscopy (FT-IR) and X-ray diffraction (XRD) analyses confirmed the physical blending of components without chemical bonding and preserved crystalline structures, respectively. The findings demonstrate that EG is an effective structural support, improving thermal stability and preventing leakage, though at the cost of reduced latent heat storage capacity.