In recent years, high-temperature water/wastewater treatment has become an emerging area of high priority interest for industries such as oil and gas, food production, and power plants, which require the separation of impurities from wastewater at elevated temperatures to recycle the treated water. However, most polymer membranes used in different membrane separation processes have poor thermal and chemical resistance, and they often soften, creep, or fail at high temperatures, reducing their performance with regard to water flux and rejection of emerging contaminants. Therefore, there is a need to develop heat-resistant polymers and membranes for treating high-temperature streams. This review paper explores the chemistry and applications of high-temperature polymers used as membranes to process wastewater and recycle water for useful purposes. The paper highlights the importance of advanced thermally stable polymer membranes in purifying wastewater at elevated temperatures and summarizes recent advances in membrane fabrication techniques, including blending, crosslinking, and nanocomposite approaches. The review also identifies future research directions in this field to meet the growing demand for sustainable water treatment solutions.