Abstract: The transition to veterancy can be psychologically challenging, and although the military provides support, the importance of social connectedness for well-being is largely unrecognised. The significance of this oversight is highlighted by the Social Identity Model of Identity Change (SIMIC), which conceptualises life change as social identity change. SIMIC has been applied to numerous life transitions, but not to veterancy, although there is evidence that the social and psychological challenges of this transition may be especially profound (e.g., due to the chronically salient, highly structured and largely unique nature of military life and identity). To remedy this, in Study 1 (N = 210), UK-based veterans completed an online survey. Consistent with SIMIC, social group maintenance and gain predicted mental health via the psychological resources they provided (meaning, self-esteem, sense of personal control), and group gain was predicted by perceived military support during the transition. Study 2 (N = 14) extended these findings qualitatively through exploration of veterans' transition experiences. These studies are the first to apply aspects of the SIMIC to the veterancy transition, and they show the applicability of SIMIC in this context. They also highlight the need for transition-related education that includes guidance on group joining and reconnecting.