This article explores the complex, and often unintended, consequences of NGO struggles to implement the normative claims embedded in discourses of liberal peace in post-conflict situations. We study Women in Black-Serbia (WIB) to examine the tensions between WIB’s adoption of a liberal, radically feminist, deterritorialized and individualistic conceptualization of peace, its development of politics and political strategies in accord with the nationalistic identities it has purported to reject, and the organization of its advocacy for peace around the memorialization of war victims. We argue, in a very polarized political climate and in the context of a heavy presence of international stakeholders, that WIB activism may produce the unintended consequence of hardening existing war identities and conflict positions. This article assesses NGOs, not mainly for the quality of their normative claims or putative roles, but as political agents whose discourses, tactics and practices are evaluated in the context of their interactions with other (local and international) actors. More broadly, this analysis illuminates the unexplored conundrums, complexities and ambiguities associated with implementation of the liberal peace in a highly polarized political space, and in the context of multi-stakeholder peace-building processes.