Abstract Strain localization and associated rheological weakening are often attributed to grain size reduction resulting from dynamic recrystallization. Most studies investigating rheological changes due to dynamic recrystallization regard recrystallized grain size as a single value that is uniquely related to stress during steady-state deformation. However, rock materials invariably exhibit a grain size distribution with distribution parameters that may be altered by dynamic recrystallization during transient deformation, affecting the rheological behaviour. This study aims to investigate the effect of deformation conditions on the evolution of grain size distribution and rheological behaviour during dynamic recrystallization in the approach to steady state. To study this, we have deformed Carrara marble to natural strains of 0.15–0.90 in axial compression at temperatures of 700–990°C, stresses of 15–65 MPa, strain rates of 3.0 × 10 −6 –4.9 × 10 −4 s −1 and a confining pressure of 150 or 300 MPa, and analysed the grain size distribution of each sample. The results show that during dynamic recrystallization, grain size distributions evolve by a competition between grain growth and grain size reduction. The relative importance of grain-size-sensitive creep increases as the average grain size is reduced with strain. Minor weakening is observed, which is probably insufficient to cause strain localization in nature.