The Citizen Initiative (CI) in the context of the legislative process is now a common mechanism in different parts of Europe and Latin America. However, it is rarely used as a participatory formula in constitution-making processes. This article documents the case of the CI (Iniciativas Populares de Norma) in Chile’s two failed constitution-making processes between 2021 and 2023, during which more than a million people actively participated in its formulation. The Chilean case matters for comparative constitutional studies due to its innovative use of technology to advance forms of digital democracy and the demonstrable impact of the CI standards on both constitutional proposals, which were ultimately rejected in the final national referendums. We argue that despite these rejections, the CI as a participatory mechanism is likely to endure over time and in future constitution-making processes. The article provides a detailed study of the Chilean experience and seeks to draw lessons for other countries’ attempts at participatory constitutional reform.