Adoption of smart energy technologies, such as electric vehicles (EVs), can significantly reduce fossil energy use, provided that adopters of an EV also use the EV in a sustainable way. Hence, it is key to understand which factors affect the likelihood that the adoption of EVs promotes the sustainable use of EVs, and promote consistent sustainable energy behaviours. We argue that the motivation to adopt an EV plays a key role in this respect. When people adopt an EV for environmental reasons, this will signal that they are a pro-environmental person, thereby strengthening environmental self-identity and promoting consistent sustainable energy behaviours. We conducted two cross-sectional studies among EV adopters to test our reasoning. As expected, the more people adopted an EV for environmental reasons, the stronger their environmental self-identity, in turn increasing the likelihood that they engaged in other sustainable energy behaviours. In contrast, adopting an EV for financial or technological reasons was not consistently related to environmental self-identity and sustainable energy behaviours. These results suggest that the motivation for adopting an EV is crucial for the likelihood that people engage in sustainable energy behaviour consistently, which is key to realise a sustainable energy transition.