Solving the world’s most pressing problems (climate change, global poverty) will require the commitment of large numbers of people. The current research draws upon the joint insights of self-determination theory and the social identity perspective to consider the mechanisms through which social interaction engenders commitment to social change. Participants (N = 137) engaged in a small group discussion to plan strategies for providing safe drinking water to people in developing countries. The degree of consensus within the interaction (regarding desired change and action to achieve that change) was measured. Multilevel path analysis showed that communication of consensus allows motives to become internalized, giving rise to new identities and commitment to social change. These results suggest that to understand how to promote commitment to social change, we need to understand the social forces that promote the formation and internalization of meaningful social identities.