An effective and just Financial Mechanism will be crucial to the success of the Global Plastic Treaty. The content in the latest Chair’s Text from INC-5.1 on finance (primarily in Article 11) could be strengthened to avoid replicating shortcomings in existing financing models, which have often been insufficient and have not always provided the necessary resources for global sustainable development. Experiences with climate finance mechanisms reveal a pattern of misdesign that needs to be addressed. The current Article 11 reflects the deep divisions evident in the two main proposals tabled at INC-5.1 in November 2024. In the light of past precedents and tensions, we argue that several core design principles related to scope, scale and social and health considerations could ensure that the Global Plastics Treaty’s Financial Mechanism supports just, ambitious and transformative global action on plastic pollution. Furthermore, we argue that several elements in the current treaty text may undermine the design and implementation of an effective and just Financial Mechanism for the future Global Plastics Treaty. These risks include overemphasizing waste management; missing connections between finance and other measures in the treaty; risks of not addressing the most effective responses; not adequately addressing plastic leakage, releases and emissions; sustaining financial investments in techno-economic lock-ins lacking sufficient safety and sustainability criteria, standards and monitoring requirements and the prospect of plastic credits, which risks repeating past false solutions. There is an opportunity for the treaty to overcome these challenges with a financial mechanism that addresses overproduction and incentivizes safer, more sustainable, accessible and cost-effective upstream solutions.