In a recently published randomized controlled trial, two-thirds of patients receiving a novel psychological treatment, pain reprocessing therapy (PRT), reported elimination or near-elimination of chronic back pain. Mechanisms of PRT and related treatments remain poorly understood but are hypothesized to center on pain reappraisal, fear reduction, and exposure-potentiated extinction. Here, we investigated treatment mechanisms from the participant perspective. A sample of 32 adults with chronic back pain who received PRT completed semi-structured post-treatment interviews about their treatment experiences. Interviews were analyzed with multiphase thematic analysis. Analyses identified three major themes reflecting participants’ understanding of how PRT led to pain relief: 1) reappraisal to reduce fear of pain, which included guiding participants to relate to pain as a helpful indicator, overcoming pain-related fear and avoidance, and reconceptualizing pain as a “sensation;” 2) the link between pain, emotions, and, stress, which included gaining insight into these connections and resolving difficult emotions; and 3) social connections, which included the patient-provider alliance, therapist belief in the treatment model, and peer models of recovery from chronic pain. Our findings support the hypothesized mechanisms of PRT centered on pain reappraisal and fear reduction, but also highlight additional processes from the participant perspective, including a focus on emotions and relationships. This study underscores the value of qualitative research methods to illuminate mechanisms of novel pain therapies. PERSPECTIVE: This article presents participant perspectives of their experience engaging in a novel psychotherapy for chronic pain, pain reprocessing therapy (PRT). Through pain reappraisal, linking pain, emotions, and stress, and connecting with their therapist and peers, many participants reported an elimination or near-elimination of their chronic back pain with therapy.