Do people have privileged and direct access to their own minds, or do we infer our own thoughts and feelings indirectly, as we would infer the mental states of others? In this study we shed light on this question by examining how mentalizing ability—the set of processes involved in understanding other people’s thoughts and feelings—relates to metacognitive efficiency—the ability to reflect on one’s own performance. In a general population sample (N = 477) we showed that mentalizing ability and self-reported socio-communicative skills are positively correlated with perceptual metacognitive efficiency, even after controlling for choice accuracy. By modelling the trial-by-trial formation of confidence we showed that mentalizing ability predicted the association between response times and confidence, suggesting those with better mentalizing ability were more sensitive to inferential cues to self-performance. In a second study we showed that both mentalizing and metacognitive efficiency were lower in autistic participants (N = 40) when compared with age, gender, IQ, and education-matched non-autistic participants. Together, our results suggest that the ability to understand other people’s minds predicts self-directed metacognition.