Self-identity is considered as a useful additional predictor in the theory of planned behaviour (TPB). However, previous research generally assessed the impact of pro-environmental self-identity in relation to single behaviours and no studies considered its potential role in moderating the impact of other predictors on behaviour. The present research used a within-persons approach to examine effects across behaviours and a longitudinal design to assess the moderating role of self-identity in the prediction of intentions and behaviours, controlling for past behaviour. Participants (N = 240) completed Time 1 questionnaires measuring TPB constructs in relation to five different pro-environmental behaviours. Two weeks later, participants (N = 220) responded to a questionnaire assessing self-reports of these behaviours during the intervening two-week period. Across pro-environmental behaviours the findings showed that pro-environmental self-identity significantly moderated the impact of perceived behavioural control on intentions and the effect of past behaviour on both intentions and behaviours.