<p>The literature distinguishes between the <i>institutional</i> and <i>ecological effectiveness</i> of international environmental organizations. The former refers to the compliance with stated objectives, the latter is about measurable improvements in environmental quality. The relationship of both concepts – and, thus, overall effectiveness – remains insufficiently understood, however. Here, we address that gap by examining the impact of institutional effectiveness on ecological performance. Leveraging data on international environmental organizations between 2008 and 2018, the findings reveal a clear link: stronger <i>institutional</i> performance correlates with <i>ecological</i> effectiveness as measured by reduced particulate pollution. By shedding light on the conditions under which international organizations drive meaningful environmental change, this research offers new insights for strengthening global environmental governance.</p>