Mineral impregnated fiber reinforcements (MIF) are an emerging alternative to conventional fiber-reinforced polymers (FRP), due to their superior thermomechanical performance at elevated temperatures. Recently, a novel type of MIF based on alkaline-resistant glass fibers and magnesium oxychloride cement has been introduced [1], providing a new perspective with regard to enhanced sustainability in the construction sector. The study at hand investigated the impact of elevated temperatures on the mechanical performance and bond behavior of mineral impregnated glass fiber reinforcements (MGF). Both the mineral impregnation and the high-strength concrete matrix are based on magnesium oxychloride cement, representing an innovative and more sustainable composite than commonly applied cementitious systems. At room temperature, the developed MGF showed outstanding mechanical properties under flexural and tensile loads, which can be attributed to the excellent mechanical properties of the individual components at room temperature, as well as the excellent fiber-matrix distribution in the prepared composites, as proven via scanning electron microscopy and computer tomography. However, flexural and tensile tests after exposure to elevated temperatures revealed a negative impact at temperatures as low as 200 °C on the used alkaline-resistant (AR-) glass fibers. This detrimental effect ultimately overshadows the enhanced thermomechanical performance of the applied mineral impregnation.