A thermal model of transform-margin evolution, including both shear heating and lateral conduction of heat from hot oceanic to colder lithosphere, was developed to gain insight into transform-margin crustal structure. Results indicate that over 2 km of crustal uplift may occur at the fault trace for a modelled transform fault 500 km in length with spreading half-rates of 1.0 and 4.0 cm/year. This uplift decreases away from the fault over a distance of 60–80 km. The viscosity of the lower continental crust and upper mantle adjacent to the transform margin is reduced by a factor of more than 100. In response to plate motion and asthenospheric upwelling at the spreading ridge, flow of this thermally weakened material may also play a role in continental crustal thinning.Thermal model predictions are compared with geological observations and crustal structure across transform margins. In particular, we show that the geology of the Southwest Newfoundland Transform Margin, eastern Canada, and the Cape Range fracture zone, Western Australia, supports the model predictions of uplift, erosion, and crustal thinning.