Although consumers’ awareness of the environmental and ethical consequences of their behaviour has grown, research on the role of multiple consumer identities in sustainability behaviours is scarce. The aim of the current study was to explain sustainable behaviour from a social identity perspective. We conducted a longitudinal cross‐national within‐subjects design consumer study in six countries (T1, N=3083; T2, N=1440). The results indicate that environmental sustainability can comprise several distinct yet overlapping sustainable behaviours. Multiple social identities seem to play different roles in these different behaviours. Therefore, efforts to enhance different sustainability behaviours are challenging yet promising. Once consumers incorporate a sustainable behaviour, it becomes part of their own identity and could lead to spill over effects on other closely related sustainable behaviours.