Based on Chinese constitutional analysis, political science, and law and society studies, we argue that work extending the application of popular constitutionalism to authoritarian states applies in Vietnam, as popular constitutionalism targets sites relevant to constitutional reform. We contend that popular constitutionalism located in authoritarian states requires three factors: a tradition of activism, space for reformist and pragmatic dialogue targeting constitutional change, and the political need for legitimacy. This article analyses activism in Vietnam, focusing on the lodging of Petition 72 with the Constitutional Amendment Drafting Commission in 2013, and the resulting responses. We conclude that this activism was pivotal in advocating for new constitutional norms, evidencing popular constitutionalism in Vietnam. The long history of Vietnamese scholar activism, the relative space for governance debates, and the political need for legitimacy made this possible. We also note that popular constitutionalism faces constraints in authoritarian states, which may shape its trajectory.