Why do some former rebels transition into social engagement after demobilisation while others do not? How do they adjust their militant aspirations to their context of reintegration? Studies on the political dimensions of rebel groups’ disarmament, demobilisation and reintegration processes have focused on post-rebel political parties, ex-combatant violence, elite transformation, political participation, and social and community engagement. Despite increased attention to reintegration processes, we know little about the processes that shape community engagement amongst ex-combatants. I address this gap by investigating the lifelong socialisation processes that influence transitions in and out of violence and social engagement. I argue that socialisation across various institutional settings in pre-recruitment and wartime life stages provides ex-combatants with dispositions and resources that, in interaction with post-demobilisation opportunities, shape their post-demobilisation social engagement. Applying a biographical approach, I analyse the trajectories of 32 ex-combatants from M-19, a left-wing nationalist guerrilla group at war with the Colombian government between 1974 and 1990. The study contributes to the literature on the long-term consequences of ex-combatant reintegration, socialisation and violence as well as the legacies of armed violence. It notably highlights how various dimensions of insurgent mobilisation can have lasting effects on individual life courses and society more broadly.