This review evaluates the performance of geopolymers in high-temperature environments, focusing on manufacturing factors such as raw material types, activators and forming processes, and the consequent properties, including mechanical properties, multi-phases and their advanced characterization techniques. It examines the influence of various raw materials on high-temperature performance, particularly the phase transformation behavior of materials with a high silicon-to-aluminum ratio. The selection of activators, such as sodium hydroxide and potassium hydroxide, and their importance in enhancing material stability and mechanical properties at elevated temperatures are also discussed. The forming processes, including foaming and microwave curing, significantly affect the density and overall performance of the resulting materials. In addition, the evolution of mechanical properties and microstructure—such as crack formation, porosity, and crystalline phase changes—is explored in relation to elevated temperatures. Advanced techniques, including transmission and scanning electron microscopy, are proven useful to investigate the correlation between microstructure and material performance. Key challenges in current research are proposed for future directions to improve the high-temperature performance of geopolymers.