Thermal Discharge from power plants in coastal waters may significantly influence the aquatic marine environment. Today, remotely sensing data is considered one of the primary sources to monitor the thermal pollution of power plants. This research quantitatively assesses the accuracy of retrieved Landsat/TIRS Sea Surface Temperature (SST) and effectively uses archival Landsat data to monitor the thermal pollution from Baniyas Thermal Power Plant (TTP) in the Syrian coastal water for 40 years from 1984 to 2023. The results show a strong linear correlation between Landsat/TIRS retrieved and in-situ measured SST values with an RMS error of 0.84 °C, which indicates the high effectiveness of using Landsat data in monitoring thermal pollution. The results also show that the average area affected by thermal pollution was 34 ha, and the thermal pollution level average was 2.9 °C. Thermal pollution changes in the entire period were analyzed according to three phases: formation and growth (1984–1992), stability (1993–2011), and decline (2012–2023). The annual thematic maps of thermal pollution show that the thermal pollution levels gradually decreased from the Baniyas TPP outlet towards open water and did not exceed a distance of 2 km offshore. The operational capacity of Baniyas TPP exhibited an influence on both thermal pollution levels and areas. The thermal pollution spatial pattern was consistent with the surface currents on the eastern coast of the Mediterranean Sea. The methodology produced in this research could be used effectively to monitor thermal pollution using satellite remote sensing data. The thematic maps developed in this study could be used as a basis for sampling to study the effect of thermal pollution levels on aquatic organisms and then develop environmental norms in Syria about the permissible values of thermal pollution.