Although the term ‘Indo-Pacific’ has become popular in the foreign policy discourse of some countries, we have yet to see any significant institution-building in the Indo-Pacific region. Borrowing insights from functional institutionalism and political leadership studies of international regimes, we introduce a ‘leadership–institution’ model to explore the problems and prospects of institutionalizing the Indo-Pacific. Through a comparative case study of the institutionalization of the Asia–Pacific vs the Indo-Pacific, we argue that two crucial factors contributed to the slow institutionalization of the Indo-Pacific as a regional system in world politics: the lack of ideational leadership from an epistemic community and the weak executive leadership from a powerful state. While ideational leaders can help states identify and expand common interests in cooperation, executive leadership will facilitate states to overcome operational obstacles in cooperation, such as the ‘collective action’ problem and the ‘relative gains’ concern. The future of institution-building in the Indo-Pacific will depend on whether and how these two leadership roles are played by scholars and states in the region. In the conclusion, we discuss the challenges of institutionalizing the Indo-Pacific and highlight China as a wild card in the future of Indo-Pacific regionalism.