According to what has recently been labeled ‘political realism’ in political theory, ‘political moralists’ such as Rawls and Dworkin misconstrue the political domain by presuming that morality has priority over politics, thus overlooking that the political is an autonomous domain with its own distinctive conditions and normative sources. Political realists argue that this presumption, commonly referred to as the ‘ethics first premise’, has to be abandoned in order to properly theorize a normative conception of political legitimacy. This article critically examines two features of political realism, which so far have received too little systematic philosophical analysis: the political realist critique of political moralism and the challenges facing political realism in its attempt to offer an alternative account of political legitimacy. Two theses are defended. First, to the extent that proponents of political realism wish to hold onto a normative conception of political legitimacy, refuting wholesale the ethics first premise leads to a deadlock, since it throws the baby out with the bathwater by closing the normative space upon which their account of political legitimacy relies. This is called the ‘necessity thesis’: all coherent and plausible conceptions of political legitimacy must hold onto the ethics first premise. Secondly, accepting this premise – and thus defending an ethics first view – does not entail that the political domain must be seen as a subordinate arena for the application of moral principles, that political normativity is reduced to morality or that morality trumps other reasons in political decision making, as claimed by political realists. Rather, the ethics first view is compatible with an autonomous political domain that makes room for an account of political legitimacy that is defined by and substantiated from sources of normativity specifically within the political. This is called the ‘compatibility thesis’.