The Regional Coordinating Unit of the Convention for Co-operation in the Protection and Development of the Marine and Coastal Environment for West and Central Africa (the Abidjan Convention) has under its wings several multilateral environmental agreements including those addressing shipping pollution. Shipping, potentially, has negative impacts on marine fauna and flora and air quality, with implications for public health. The Regional Coordinating Unit seeks to strengthen implementation of the Abidjan Convention by party-states through co-operation with state actors using various pathways based on its internal resources and competencies but the Unit is also starting to explore engagement with potential non-state actors. The ability of the Unit to exert influence on implementation is constrained by domestic politico-administrative institutions. This paper seeks to understand the influence of the Regional Coordinating Unit on the implementation of the Abidjan Convention in the field of shipping pollution. It uses three theoretical perspectives for the analysis: the influence of international environmental bureaucracies, domestic regulatory-politics and transnational governance. The paper shows how these theories are complementary because the influence of international bureaucracies such as the Regional Coordinating Unit cannot be adequately understood through factors internal to their organisation alone but needs to be analysed in relation also to external factors, both domestic politico-institutional ones in states that international bureaucracies work with, and the role of relevant non-state actors in the implementation of multilateral environmental agreements. It is concluded that, although influence cannot be measured directly, it is likely that Regional Coordinating Unit’s influence through its autonomy-centred efforts are quiet strong but negatively constrained by the traditional state-centric responsibility for implementation of international legal instruments where domestic regulatory-politics lack sufficient political will and support from and engagement with non-state actors.