In this paper, we propose that environmental pioneers can drive sustainable change by adopting an ideological minority position that accentuates the group's positive distinctiveness as sustainability-oriented, and influence the group towards more sustainable norms and practices. We studied 107 Dutch-speaking participants engaging in three online small-group discussions. We examined the extent and processes of change instigated by a vegan confederate in the discussion groups, with a longitudinal design with 4 time points (pre-discussion and after each session). In contrast to earlier findings suggesting that vegans typically evoke resistance, the results of our studies demonstrate a shift towards veg*nism in group members' individual attitudes, behaviors, and biospheric values over time. Moreover, depending on whether groups valued diversity or similarity (manipulated experimentally), we identified two change trajectories toward perceived sustainable group norms: A gradual, reflective process, in which groups elaborate on the vegan perspective, and slowly move towards this perspective (consistent with conversion theory) in groups valuing diversity, and a more rapid trajectory resembling a process of conformity to a ‘prototypical’ vegan pioneer in groups valuing similarity. Zooming in on the group dynamics revealed that consensualisation predicts norm perceptions in both conditions, but conformity pressure is only predictive insimilarity-valuing groups.