Theories of Multi-Level Governance (MLG) assert that power in modern governance is no longer limited to the nation-state but distributed vertically across levels, such as international Regional Organisations (ROs), and horizontally to include non-state actors like civil society. Public Administration research highlights that involving citizens in decision-making enhances transparency, accountability, and trust in institutions. As ROs take on central roles in addressing global challenges, understanding how they engage citizens is increasingly important. Yet, citizen participation mechanisms in ROs remain underexplored or limited to small-n studies. Recent studies reveal that only one-third of RO founding treaties reference citizen engagement, with considerable variation in the mechanisms developed. This raises a critical question: What conditions influence the development of citizen participation mechanisms in ROs?

Building on theories of RO life-cycles, which call for closer examination of evolving institutional characteristics and performance, this study uses regression analysis to test different hypotheses drawn from literature on non-state actor involvement in governance. The analysis covers 70 ROs from 1945 to 2016. As a dependent variable, this paper develops a new Indicator of Citizen Participation in ROs (ICPRO), which measures access to information, elections, and consultations. Analysed alongside established indicators, such as the Measure of International Authority (MIA) and Legitimation Strategies of Regional Organisations (LegRO), preliminary findings reveal significant links between institutional power and participatory governance mechanisms. This research offers actionable insights for policymakers to enhance RO legitimacy and effectiveness through citizen engagement, offering a pathway for more inclusive governance.