Purpose: Adults with diabetes mellitus (DM) suffer often from chronic pain, yet evidence-based interventions for comorbid pain and DM are scarce. We tested the effect of a peer-led cognitive behavioral training (CBT) intervention on pain self-efficacy (PSE), pain intensity, and pain-related functional limitations (PRFL) in adults with DM, 1 year after trial initiation. Methods: The yearlong “Living Healthy” cluster-randomized trial included 230 residents of rural Alabama with DM, who reported pain in the past month; communities were treated as clusters. Intervention participants received a peer-delivered 8-session structured CBT intervention in the context of diabetes self-management; attention control arm participants received a peer-delivered 8-session general health education program. Outcomes included PSE (Arthritis Self-Efficacy Scale, range 10-100); pain intensity (McGill Pain Questionnaire, range 0-45); and PRFL (Western Ontario and McMaster Universities Osteoarthritis Index scale, range 0-100). We examined control-intervention differences in changes in outcome scores from baseline to 3-month and 12-month follow-up, adjusted for clustering. Findings: The 195 participants with follow-up data were aged 59 ± 10.4 years, 96% were African American, 79% were women, and 80% reported pain on the day of baseline data collection. At 3-month follow-up, PSE increased more for intervention (21-point increase) than control (5-point increase) participants (P for control-intervention (C-I) difference in change <.001); pain intensity decreased for both groups; and PRFL decreased only for intervention participants (–11 score; P for C-I difference in change <.001). Results were sustained at 12 months, and pain intensity significantly improved in only the intervention arm (P for C-I difference in change =.01). Conclusions: This peer-delivered CBT intervention improved pain self-efficacy, pain-related functional limitations, and pain intensity over 12 months among rural participants with DM and chronic pain.