As mindfulness-based cognitive therapy (MBCT) becomes an increasingly mainstream approach for recurrent depression, there is a growing need for practitioners who are able to teach MBCT. The requirements for being competent as a mindfulness-based teacher include personal meditation practice and at least a year of additional professional training. This study is the first to investigate the relationship between MBCT teacher competence and several key dimensions of MBCT treatment outcomes. Patients with recurrent depression in remission (N = 241) participated in a multi-centre trial of MBCT, provided by 15 teachers. Teacher competence was assessed using the Mindfulness-Based Interventions: Teaching Assessment Criteria (MBI:TAC) based on two to four randomly selected video-recorded sessions of each of the 15 teachers, evaluated by 16 trained assessors. Results showed that teacher competence was not significantly associated with adherence (number of MBCT sessions attended), possible mechanisms of change (rumination, cognitive reactivity, mindfulness, and self-compassion), or key outcomes (depressive symptoms at post treatment and depressive relapse/recurrence during the 15-month follow-up). Thus, findings from the current study indicate no robust effects of teacher competence, as measured by the MBI:TAC, on possible mediators and outcome variables in MBCT for recurrent depression. Possible explanations are the standardized delivery of MBCT, the strong emphasis on self-reliance within the MBCT learning process, the importance of participant-related factors, the difficulties in assessing teacher competence, the absence of main treatment effects in terms of reducing depressive symptoms, and the relatively small selection of videotapes. Further work is required to systematically investigate these explanations.