<p>A hard, wear-resistant surface layer on a steel component can be obtained efficiently by laser transformation hardening (LTH) process. It involves the ultrafast heating action of a high-energy scanned laser beam on the steel surface, followed by self-quenching cooling through conduction. Among others, the initial microstructure of steel plays a very significant role in the nucleation and growth kinetics of austenite formation during ultrafast laser heating. Severe plastic deformation (SPD) can produce a microstructure with numerous crystalline defects. Thus, SPD can serve to make an interesting microstructure as an initial microstructure for LTH. In the present work, severe plastic deformation of low-carbon low-alloy steel specimens containing four different tempered martensitic structures was performed to produce four different initial microstructures for LTH process. Specimens of AISI 8620 steel were used for investigation. Tempering was done at four different temperatures before severe plastic deformation. After SPD specimens were subsequently surface hardened by LTH treatment. The effect of these initial microstructures on LTH was investigated using optical microscopy, electron microscopy, micro-hardness traverse, and XRD. Lath martensitic features such as prior austenite grain size, packet size, and block width become much finer for the specimens laser treated after SPD compared to conventional LTH. Due to these microstructural refinements, the specimens subjected to SPD before LTH showed significant improvement in surface hardness (20%) and hardening depth (22%) in comparison with the specimens subjected to conventional LTH.</p>