This article aims to explain the multilateral negotiations of the Treaty on the Prohibition of Nuclear Weapons, which was adopted at the UN General Assembly on July 7, 2017, from the model of institutional bargaining. Its findings are: first, non-nuclear states’ sense of frustration and crisis about the failure of progress on nuclear disarmament under the NPT regime served as a critical momentum to move towards the negotiations. Second, consensual knowledge about the humanitarian effects of nuclear weapons and solutions served as a driving force behind embarking on the negotiations. Third, the leadership by a core group of pro-ban non-nuclear countries was effective in mobilizing political support and facilitating the timely conclusion of the negotiations. Fourth, a salient solution of a simple and robust treaty, and a bridging solution to allow any country in possession of nuclear weapons to join the treaty before their elimination contributed to the prompt agreement on the treaty. Fifth, clear and effective compliance measures regarding non-nuclear states facilitated the conclusion of the negotiations, whereas the lack of clear and effective compliance measures regarding state parties possessing nuclear weapons rather contributed to the timely end of the negotiations. Finally, a fast-track approach, a single-text negotiating strategy, and an issue decomposition strategy were effective in reaching consensus on the treaty text.