A key actor is missing in transitional justice discourse. While ex-combatant issues and DDR processes generate rich literatures, transitionary armed opposition groups as such are neglected. Instead, the discourse ‘sees’ only forms of mobilisation that fit dominant narratives, with neat categories of victim and perpetrator. This paper addresses these research gaps, drawing on social movement theory and de-centred transitional justice literature to develop and ground a model for analysis of armed opposition groups transitioning from violence. A theoretical framework is outlined, emphasising such groups’ agency, yet locating them ambiguously on a victim-perpetrator dyad. The framework is grounded using a Northern Ireland case-study. The process placed a political party (Sinn Féin (SF)) linked to an armed opposition group (Irish Republican Army (IRA)) at a new political dispensation’s centre. Three qualitative datasets are employed: (1) IRA public statements from 1994- ; (2) SF electoral manifestos; and (3) interviews with mid-ranking former IRA prisoners. Transitional justice poses acute dilemmas for such movements. To meet the expectations of its targets of mobilisation. the movement’s framing will insist upon post-conflict accountability for state violations (truth commissions, trials etc). But the movement may well find also itself the object of scrutiny.