The primary objective of this study is to investigate the effects of thermal curing and fly ash incorporation on the mechanical and physical properties of reactive powder concrete (RPC) to develop a more sustainable RPC mixture with partial replacement of ordinary Portland cement (OPC) by fly ash. Four mixes were prepared: a reference mix (R) and mixes with fly ash replacement levels of 10%, 20%, and 30% (RF10, RF20, and RF30). Each mixture was cast and tested in three specimens for each age of testing. The specimens were thermally cured at 70°C for 5 hours per day for a total of 3 days, followed by water curing until the testing age. The experiments showed that adding 20% fly ash improved the overall performance of RPC. The RF20 mix showed the best compressive strength, with increases of 3.39%, 4.47%, and 4.86% at 7, 28, and 56 days, respectively, relative to a reference mix. Furthermore, flexural strength and splitting tensile strength increased by 2.39% and 1.69%, respectively, at 28days. The RF20 mixture had the highest dry density (2683 kg/m³), the lowest water absorption (0.114%), and the lowest porosity (1.75%). However, a 30% replacement of cement with fly ash reduced mechanical properties. Results indicated that 20% fly ash inclusion under thermal curing conditions could effectively improve RPC performance and promote sustainability by reducing cement use.