Partnerships between companies and NGOs have received considerable attention in CSR in the past years. However, the role of NGO legitimacy in such partnerships has thus far been neglected. We argue that NGOs assume a status as special stakeholders of corporations which act on behalf of the common good. This role requires a particular focus on their moral legitimacy. We introduce a conceptual framework for analysing the moral legitimacy of NGOs along three dimensions, building on the theory of deliberative democracy. Against this background we outline three procedural characteristics which are essential for judging the legitimacy of NGOs as potential or actual partners of corporations.