OBJECTIVE: Despite the heightened urgency of the current prescription opioid crisis, few psychotherapies have been evaluated for chronic pain patients receiving long-term opioid analgesics. Current psychological pain treatments focus primarily on ameliorating negative affective processes, yet basic science suggests that risk for opioid misuse is linked with a dearth of positive affect. Interventions that modulate positive psychological processes may produce therapeutic benefits among patients with opioid-treated chronic pain. The aim of this study was to conduct a theory-driven mechanistic analysis of proximal outcome data from a Stage 2 randomized controlled trial of Mindfulness-Oriented Recovery Enhancement (MORE), an integrative intervention designed to promote positive psychological health. METHOD: Patients with opioid-treated chronic pain (N = 95; age = 56.8 ± 11.7; 66% female) were randomized to 8 weeks of therapist-led MORE or support group (SG) interventions. A latent positive psychological health variable comprised of positive affect, meaning in life, and self-transcendence measures was examined as a mediator of the effect of MORE on changes in pain severity at posttreatment and opioid misuse risk by 3-month follow-up. RESULTS: Participants in MORE reported significantly greater reductions in pain severity by posttreatment (p = .03) and opioid misuse risk by 3-month follow-up (p = .03) and significantly greater increases in positive psychological health (p < .001) than SG participants. Increases in positive psychological health mediated the effect of MORE on pain severity by posttreatment (p = .048), which in turn predicted decreases in opioid misuse risk by follow-up (p = .02). CONCLUSIONS: Targeting positive psychological mechanisms via MORE and other psychological interventions may reduce opioid misuse risk among chronic pain patients receiving long-term opioid therapy. (PsycINFO Database Record (c) 2019 APA, all rights reserved).