Building on previous studies, we propose a robust estimation strategy to uncover the causal effects of tax administration strength on tax revenue in 121 countries over the period 2014–2022. Our novel approach utilizes a unique expert survey to construct an Operational Strength Index of tax administration, using the International Survey on Revenue Administration (ISORA), and employs an instrumental variable strategy based on the IMF Fiscal Affairs Department’s Capacity Development programs. We find that strengthening tax administration significantly boosts tax revenue, particularly in emerging and developing economies, and especially in countries with lower levels of informality, stronger institutions, and higher financial development. These findings carry important policy implications for governments and development partners aiming to enhance tax administration capacity and strengthen public finances overall.