States are on the brink to start negotiations on a global agreement on plastic pollution. In this context, scientists, policymakers and stakeholders voiced requests for strengthening and improving the knowledge base. These requests often include demands for a scientific advisory mechanism or body that operates as two-way interface between science and policy and that informs policy- and decision-making in the global combat against plastic waste in the oceans and the need for a life cycle approach to marine plastic pollution that covers all stages in the plastics life cycle. The report makes the case for a global scientific mechanism on marine litter and microplastics and discusses the conditions to make it work effectively and to enable it to strengthen the global science and knowledge base on marine litter and microplastics.