Abstract This article explores the dilemmas of progressive legalism during the Vietnam War years (1965–1975) by investigating the history of the Russell Tribunal. Scholars have argued that the 1960s witnessed a flourishing of anticolonial legalism, as activists sought to purge international law of its imperial origins. However, as the history of the Russell Tribunal shows, the transformation of law from a handmaiden of empire into a tool of anti-imperial resistance was not straightforward. This article examines the strategies employed by activists to overcome international law’s imperial biases. It argues that activists focused on developing a ‘jurisprudence for the future’, a mode of activism aimed at constructing international rules and norms that challenged, rather than sustained, European domination. By advocating for a future-oriented activism, tribunal members sought a temporary solution to the predicament of law’s imperial leanings. They defended their use of international law by asserting that their protests would contribute to the emergence of a future and more emancipatory international law. Nevertheless, an examination of the World Tribunal on Iraq (2003–2005) reveals that this envisioned future international law has yet to materialize. This article highlights the significance of futurism in the history of anticolonial lawyering and suggests that scholars should evaluate the limitations of a future-oriented legal activism.