The ability to accurately monitor the quality of one's choices, or metacognition, improves under speed pressure, possibly due to changes in post-decisional evidence processing. Here, we investigate the neural processes that regulate decision-making and metacognition under speed pressure using time-resolved analyses of brain activity recorded using electroencephalography. Participants performed a motion discrimination task under short and long response deadlines and provided a metacognitive rating following each response. Behaviourally, participants were faster, less accurate, and showed superior metacognition with short deadlines. These effects were accompanied by a larger centro-parietal positivity (CPP), a neural correlate of evidence accumulation. Crucially, post-decisional CPP amplitude was more strongly associated with participants' metacognitive ratings following errors under short relative to long response deadlines. Our results suggest that superior metacognition under speed pressure may stem from enhanced metacognitive readout of post-decisional evidence.