This mixed-methods pilot study aimed to assess the symptomatic changes of post-traumatic stress disorder, complex post-traumatic stress disorder, dissociative symptoms, self-critique, and self-compassion following participation in a 16-week trauma-sensitive mindfulness and compassion intervention. The adverse experiences of participation were also explored explicitly. Seventeen predominantly female clients with severe post-traumatic stress disorder symptomatology participated in the trauma-sensitive mindfulness and compassion intervention. All clients completed questionnaires before (pre) and after (post) the intervention to gain information on symptom change, self-critique, and self-compassion. Second, a qualitative interview addressing clients’ experiences of participation, including an explicit focus on adverse experiences, was conducted. There was a significant decrease in PTSD, CPTSD, dissociative symptoms, self-hatred, and inadequate self before and after the intervention. All the clients reported having adverse experiences during participation but no lasting negative effects. The results point to the potential of the TMC intervention in helping reduce trauma symptoms and self-critique while also elucidating the tremendous stress that clients with trauma experience undergoing trauma treatment. However, no injurious adverse effects were reported. These preliminary results warrant further investigation via a randomized control trial to examine the efficacy of TMC. The study is registered in ClinicalTrials.gov ID: NCT05993468.