The Geneva Declaration on Human Rights at Sea is a recent initiative of the non-governmental organization (NGO), Human Rights at Sea, and provides an opportunity to examine how an NGO-led initiative may contribute to international law-making. This article compares the Geneva Declaration to other NGO-led endeavours that resulted in the adoption of international treaties, including the Ottawa Convention, Cluster Munitions Convention, and Nuclear Weapon Ban Treaty. It also assesses how NGOs may contribute to the development of informal agreements that influence state decision-making. In doing so, the discussion draws on interviews with the drafters of the Geneva Declaration to further assess the possible trajectory of the instrument in international law-making. The experience of Human Rights at Sea in developing the Geneva Declaration provides a striking example of the current potential and limits of civil society actors in international law-making.