Permeability, diffusivity, and solubility of deuterium in the low-activation martensitic stainless steel EUROFER97 were derived from measurements of gas permeation in the transient and steady-state regimes at temperatures from 100 to 350°C and at pressures from 2 × 103 to 2 × 105 Pa. The specimens were used in four conditions to investigate the effect of irradiation-induced defects: standard annealed condition, preirradiated with protons, implanted with helium, and implanted plus annealed to produce helium bubbles. In general, displacement defects as well as implanted helium tend to decrease permeation and diffusivity. Permeation and diffusion measurements were also performed under simultaneous irradiation, showing no net effect if the slight temperature increase due to irradiation is taken into account. Diffusion measurement of implanted hydrogen gave equal or slightly lower values than gas permeation, which is in qualitative agreement with results from preirradiated specimens. Trapping parameters are derived by a detailed comparison to a saturable-trap model. Results are compared to previous studies on 7%Cr F82H and 11%Cr MANET-II steels, and effects of compositional variations are indicated.