Dodecyl alcohol (DDA) is a promising solid-liquid phase change material (PCM) due to its favorable latent heat storage (LHS) characteristics. However, the leakage issue of PCM in a melted state during the heating period and low thermal conductivity restricts its utilization potential in thermal energy storage (TES) practices. Within the same context, the present work aims to overcome the leakage issue and improve the thermal conductivity of the DDA. With this in mind, a novel leak-proof layered double hydroxide (LDH)/DDA composite PCM is proposed through a solution-based impregnation method. The leak-proof impregnation ratio of the DDA impregnated within the cavities of the synthesized Al/Fe-LDH was determined to be 60%. Detailed morphological, physicochemical, and thermal properties of the fabricated composite were studied by scanning electron microscopy (SEM), Fourier transforms infrared (FTIR) spectroscopy, X-ray diffraction (XRD) spectroscopy, differential scanning calorimetry (DSC), thermalgravimetric analysis (TGA), and thermal cycling study. The results show that the LDH/DDA composite has a suitable phase change temperature (about 20°C) for passive solar thermal management of building envelopes. This composite PCM showed high LHS enthalpy (about 136 J/g), good thermal stability, and cycling LHS reliability. It also showed nearly 152% higher thermal conductivity compared to that of pure DDA, ultimately reducing the melting and solidification time of the pure DDA by 44.9% and 45.5%, respectively.