This paper will examine the ways in which peace settlements are producing a lex pacificatoria, a new 'law of the peacemakers', in a range of different areas relating to international conflict and security law. The essay illustrates how the practice of fashioning and implementing peace settlements is forcing a revision of relevant international law, as the traditional assumptions and boundaries of the relevant bodies of law do not fit within post-settlement political landscapes, are inadequate for enabling and regulating peace settlement implementation and do not contain guidance for the dilemmas faced post-settlement. The paper describes the ways in which a lack of fit between peace settlement dilemmas and international legal doctrines have generated new practices and new articulations of how international legal regimes regulate settlement implementation. Building on earlier arguments, I argue that these revisions constitute a new lex pacificatoria, or 'law of the peacemakers', in the form of a normativized practice of conflict resolution. The extent to which these new practices constitute 'law' at all is critically evaluated throughout the chapter. In conclusion, I consider whether it is possible, useful and desirable to frame and develop the 'new law' as a new jus post bellum drawing across existing regimes, to supplement the jus ad bellum and jus in bello.