This study presents the development of form-stable eutectic mixtures, modified with nanoscale structures for enhanced thermal performance. These additives may result in the next generation of phase change materials (PCMs) for thermal energy storage systems. An appropriate gelling or thickening agent (2-hydroxypropyl ether cellulose) is introduced so that the PCM will lose its fluidity, become form-stable, and the liquid leakage problem will be overcome. Nano-graphene platelets (NGPs) are added in order to enhance the thermal properties and overall heat transfer. Differential scanning calorimetry (DSC) was carried out for the thermal analysis of the PCMs. The paper experimentally studied in detail the enhanced thermo-physical properties required for stimulating and modelling the PCM in energy storage applications such as specific heat, thermal diffusivity, thermal conductivity, enthalpy, and density. The principle of the T-history method was applied using a parallel plate heating/cooling guarded plate apparatus to determine the true phase transition temperatures of bulk PCM. The supercooling of the enhanced shape stable mixture was found to be less than 0.1 °C. The thermal reliability test indicated that the enhanced form-stable eutectic mixture had reliable thermal performance over a postulated lifetime of 80 years. As a result, the developed form stable PCM eutectic mixture is a promising material for thermal energy storage.