The suppression of inappropriate actions is critical for flexible behavior. Cortical-basal ganglia networks provide key gating mechanisms for action suppression, yet the specific roles of neuronal subpopulations are poorly understood. Here, we examine Arkypallidal (“Arky”) and Prototypical (“Proto”) globus pallidus neurons during a Stop task, which requires abrupt cancellation of an imminent action. We first establish that Arky neurons can be identified by their firing properties across the natural sleep/wake cycle. We then show that Stop responses are earlier and stronger in the Arky compared to the Proto subpopulation. In contrast to other basal ganglia neurons, pallidal Stop responses are selective to Stop, rather than Go, cues. Furthermore, the timing of these Stop responses matches the suppression of developing striatal Go-related activity. Our results support a two-step model of action suppression: actions-in-preparation are first paused via a subthalamic-nigral pathway, then cancelled via Arky GABAergic projections to striatum. •Rapid stopping of imminent actions depends on complementary basal ganglia mechanisms•A fast pause process buys time for more selective cancellation via globus pallidus•Arkypallidal neurons quash action representations that are developing in striatum•Arkypallidal neurons can be identified by their firing across the sleep-wake cycle The ability to suppress imminent actions is a hallmark of executive control. Mallet, Schmidt et al. decompose this function into complementary Pause and Cancel mechanisms, the latter achieved via a subclass of globus palidus neurons that selectively inhibit striatum.