This investigation examines the strain-rate-dependent mechanical response of as-received and post-weld heat treated 2.25Cr1Mo0.25V steel across quasi-static (0.0003–0.01 s−1) and dynamic regimes (1100–2500 s−1), employing tensile testing by using Hopkinson tension bar and electronic tensile machine. The ductility and strength, as well as the effect of heat treatment were investigated. The results indicate that the ductility has two regimes, where failure strains remain rate-insensitive under quasi-static loading but increase at dynamic rates. Moreover, the flow stresses increase monotonically with rising strain rates, whereas the strain rate sensitivity is non-monotonic, exhibiting an increasing trend with rising strain rates below 1000 s−1, followed by reductions at higher rates. Post-weld heat treatment (PWHT) enhances ductility but reduces strength. In addition, the values of the strain rate sensitivity at all strain rates rise after PWHT.