What, if anything, can transnational advocacy networks (TANs) contribute to the democratization of public spheres outside Westphalian frameworks? On the one hand, TANs excel at turning international public campaigns into political influence – connecting people and power across borders. On the other hand, the increasingly policy‐orientated nature of TANs raises questions about their legitimacy in speaking on behalf of multiple publics. In this article, I suggest that a TAN's success in ensuring the political efficacy of public spheres, while at the same time undermining their normative legitimacy, reflects two sides of the same coin. This is a consequence of the recent internal professionalization of advocacy networks. Framing professionalization as a particular form of communicative distortion within TAN decision‐making, I suggest that networks should incorporate internal deliberative mechanisms, adapted from international social forums, to enhance the normative legitimacy of democratic public spheres.