Non-state actors are playing an increasing role in global environmental governance. Elucidating the modalities and implications of this engagement is important to understanding international policy-making processes. CITES, the Convention on International Trade in Endangered Species of Wild Fauna and Flora, is the primary mechanism for regulating international wildlife trade. It functions by listing species in its Appendices with corresponding trade controls. Accurately listing species in the Appendices is therefore fundamental to the Convention’s effectiveness. We investigate the influence of non-state actors on amending the CITES Appendices using an established framework for assessing NGO influence in international environmental negotiations. We find that non-state actors have been successful in issue framing and agenda setting, and in influencing the position of other actors and final decisions. We also find evidence that NGOs have sought to abuse CITES in pursuit of “campaign” victories, including claiming unwarranted victories, thus undermining NGO legitimacy and accountability. We recommend that the CITES parties seek the most robust science to inform decision-making on proposed amendments to the appendices, which should be broadened to include socioeconomic and economic considerations in order that proposals are evaluated in their real-world context. We further recommend that NGOs should seek to fully understand decision-making in the Convention in order to maximise their legitimate contribution to CITES. Further research is needed to fully elucidate the influence of non-state actors in CITES.