This article investigates the drivers of the parliamentarisation of war powers. Building on recent findings in the study of war deployments, we argue that the existing literature has predominantly focused on parliamentary drivers of parliamentarisation, leaving potential executive interests untouched. To fill this gap, we propose a rational choice institutionalist-based framework for identifying the motivations and strategies of both parliamentary and executive actors in episodes of parliamentarisation. We apply this novel heuristic device to the case of Belgium and the parliamentary approval of the military interventions in Libya (2011) and Iraq (2014-) more in particular. Building upon data from interviews and document analysis, we show that stronger parliamentary involvement in the decision about military deployment is not just the result of increased parliamentary pressure, but equally, and perhaps most importantly, of the willingness and strategy of the executive to seek legitimacy or support.