This paper presents a multiphysics investigation of the effectiveness of textile-reinforced concrete (TRC) composite modified by the addition of phase change materials (PCMs). The potential of this composite lies in the combination of the lightweight characteristic of TRC with the heat storage capacities provided by PCMs. This study focuses on the effects of PCMs on both the mechanical and thermal performances of TRCs. The efficiency of an innovative concept of PCM–TRC slab resulting from the reinforcement of a PCM modified matrix with a textile grid is mechanically and thermally evaluated. Despite the degradation of the mechanical performance of PCM–TRC slabs with PCM content, the ductile and multicracking behaviors of the slabs are conserved. The temperature and thus the PCM state (solid or liquid) affect the mechanical performance of the PCM–mortar matrix and PCM–TRC slabs. This can be attributed to the PCM volume change that occurs during phase change. In terms of thermal performance, in comparison with the reference TRC slab, the 10 wt% PCM–TRC slab (4.5 cm thick) results in an energy saving of 37% and a temperature decrease of 4 °C at the peak.