The deformation behaviour of a newly developed alumina-forming austenitic (AFA) stainless steel at elevated temperatures was investigated. It was found that the steady-state data could be well described by a stress power law that considered the threshold stress and temperature dependence of the shear modulus and self-diffusion coefficient, suggesting that the deformation of the austenite matrix was controlled by the lattice self-diffusion. The threshold stress was temperature-dependent and appeared to be caused by Orowan bowing stress. At temperatures below 1023 K, the secondary NbC phase was the major hardening precipitate, but at temperatures above 1023 K, the Laves Fe₂Nb phase became dominant. The apparent interaction energy required for mobile dislocations to overcome the particle obstacles decreased from 163 to 34 kJ/mol with increasing temperature, which was most likely associated with the formation of the two different precipitates.