Individuals suffering from borderline personality disorder (BPD) experience difficulties with mindfulness. How mindfulness influences BPD symptoms, however, is still unknown. We hypothesized that the relationship between mindfulness and BPD symptoms would be mediated by self-compassion. In study 1, we recruited 29 individuals with BPD and 30 group-matched healthy controls. In study 2, we complemented our results with findings from a larger, nonclinical sample of 89 participants that were recruited during an open-house event at the local university. All participants completed questionnaires assessing self-compassion, mindfulness, BPD symptom severity, and emotion dysregulation. In both studies, self-compassion mediated the relationship between mindfulness and BPD symptom severity as well as between mindfulness and emotion dysregulation. Self-compassion seems to be one psychological process that could explain the relationship between mindfulness and BPD symptoms. One promising approach in therapy could be to target self-compassion more directly during mindfulness trainings and interventions.