Field sites and key actions observed.

This study presents the first ethnographic investigation of scientist climate activism, addressing a major gap in understanding how scientists navigate tensions between professional norms of neutrality, objectivity, and activism over time. Drawing on two years of immersive, longitudinal ethnography with Scientists for Extinction Rebellion in the UK, this study provides a rigorous, process-based account of how scientists enter activism, manage identity conflicts, and negotiate their boundaries of engagement. Findings show that identity-aligned spaces legitimise initial participation and foster belonging. Scientists strategically draw on professional expertise and scientific symbols (e.g., lab-coats, peer-reviewed papers) to legitimise action and engender collective identification. However, these same symbols can also limit participation to those who identify with them and generate expectations of universal expertise. Over time, activism reshapes professional identity, reinforcing moral conviction and producing hybrid scientist-activist identities. Sustained commitment depends on collective efficacy, peer affirmation, and care practices that support autonomy and buffer burnout. Escalation is non-linear: willingness to take risks increases with experience, yet professional, personal, and ethical considerations also influence decisions. By mapping critical moments in scientists’ activist trajectories, this study advances social psychological models of identity conflict by demonstrating how professional norms, moral commitments, and collective actions dynamically interact over time. It introduces the concept of hybrid scientist-activist identity formation as a process, providing original, rigorous, and significant insights that extend theory and inform strategies for effective scientist advocacy.