Achieving sustainable development and meeting the UN Sustainable Development Goals requires that there be an effective process of negotiating and implementing sustainable development policies and practices. This paper characterizes an evolving approach that we define as sustainable development diplomacy. Based on an analysis of the history of climate governance as a case study of sustainable development diplomacy and drawing on a diverse range of literatures including international negotiations, global environmental governance, and socio-ecological systems, it identifies seven diagnostics that can be used to evaluate the negotiation and implementation of sustainable development goals. We argue for a needs-based approach that brings together diverse stakeholders to devise flexible solutions that fit the complexity and scale of sustainable development challenges. We illustrate the diagnostic elements with examples from our case study of climate change, as one of the major global sustainable development challenges, but the diagnostics have wider applicability to sustainable development diplomacy and practice more generally.