Geopolymers, typically, are created by blending aluminosilicate with a concentrated alkali hydroxide or an alkaline silicate medium, and then undergo a curing process at room temperature or slightly higher. The formation of geopolymers includes a combination of solid and liquid components . The solid part comprises aluminosilicate sources in powder form, containing a proper ratio of highly reactive silica and alumina. This study investigated a metakaolin-based geopolymer blended with Oujda clay, replacing 5–15 wt% of MK. The research delved into the structural, thermal stability, and microstructural changes in the geopolymer pre- and post high-temperature exposure, using X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). Thermal treatment of Oujda clay was conducted, and the optimal conditions were determined as calcination at 800°C for 3 hours. It was observed that the addition of Oujda clay enhanced the compressive strength of the geopolymer by expediting the reaction process activated by the alkalis. After 28 days of curing, the compressive strength increased by 31% with 15% by weight of Oujda clay. The high chemical activity of Oujda clay accelerated the geopolymerization process at high temperatures and facilitated the healing of microcracks. Moreover, Oujda clay improved the formation of a compact ceramic protective layer, thereby preventing the geopolymer from disintegrating at elevated temperatures.