Severe plasma transients such as disruptions will impose high magnitude, short duration thermal loads on the plasma-facing first wall of the EU’s DEMOnstration tokamak. Repeated over DEMO’s lifetime, these transients may cumulatively alter the microstructure of first wall structural materials, degrading their performance. The effects of repeated mitigated disruptions on the microstructure of the reduced activation ferritic/martensitic steel Eurofer 97 is reported. Time-dependent finite element thermal analysis of mitigated disruption heating on DEMO’s water-cooled lithium lead (WCLL) blanket concept has been used to design a novel laser-based transient thermal exposure experiment. The microstructural evolution of Eurofer 97 under these dynamic thermal loads has been studied via a variety of scanning and transmission electron microscopy techniques, and micromechanical testing. Just one 700°C thermal transient was found to promote grain coarsening and partial recrystallisation. Further exposure resulted in significant grain growth and a reduction of grain aspect ratios. The nucleation and coarsening of Cr23C6 at grain boundaries and V-rich and Ta-rich MX precipitates within the ferritic matrix was also observed. The microstructural evolution resulting from 850°C transients is also reported. After 1000 transients at 850°C, Eurofer 97’s hardness was decreased by 32%.