In recent years, mindfulness and compassion-based interventions (MCBI) have been found to beneficially influence the acquisition of essential skills in psychotherapy and are a promising way to improve relationships with patients. In this regard, new studies are needed to evaluate the effects of MCBI on psychotherapists and their patients and to analyze the influence of these effects on the processes and outcomes of psychotherapy. In this randomized controlled trial, we evaluate the efficacy of an MCBI in psychotherapists' mindfulness skills and self-reported empathy, as well as its indirect effect on patients (patient-reported psychotherapists' empathy, therapeutic bond, and symptomatology). Finally, we present a multilevel structural equation model (MSEM) to analyze the relationship between these variables in psychotherapists and their patients. A group of psychotherapists (N = 63) were randomized to an MCBI or an active control group (empathy diary). We assessed psychotherapists and their patients (N = 121) before and after the MCBI and at follow-up evaluation. Psychotherapists' results showed an increase in psychotherapeutic mindfulness skills (PMS) after the MCBI and at follow-up, whereas self-reported empathy improved at follow-up. Patients' results showed an improvement in perceived empathy, therapeutic bond, and symptomatology after the MCBI. The improvements in symptomatology were maintained for somatization and anxiety at follow-up. According to the MSEM, the increase in PMS is related to an increase in patient-reported psychotherapists' empathy, which produces an improvement in therapeutic bond and their symptomatology. These results support the benefits of introducing MCBI in psychotherapists' training to improve the psychotherapy outcomes. (PsycInfo Database Record (c) 2023 APA, all rights reserved).