Background: Mental health problems are common among people with diabetes. However, evidence-based strategies for the prevention and early intervention of emotional problems in people with diabetes are lacking. Our aim is to assess the real-world effectiveness, cost-effectiveness, and implementation of a Low-Intensity mental health Support via a Telehealth Enabled Network (LISTEN), facilitated by diabetes health professionals (HPs). Methods: A hybrid type I effectiveness-implementation trial, including a two-arm parallel randomised controlled trial, alongside mixed methods process evaluation. Recruited primarily via the National Diabetes Services Scheme, Australian adults with diabetes (N = 454) will be eligible if they are experiencing elevated diabetes distress. Participants are randomised (1:1 ratio) to LISTEN—a brief, low-intensity mental health support program based on a problem-solving therapy framework and delivered via telehealth (intervention) or usual care (web-based resources about diabetes and emotional health). Data are collected via online assessments at baseline (T0), 8 weeks (T1) and 6 months (T2, primary endpoint) follow-up. The primary outcome is between-group differences in diabetes distress at T2. Secondary outcomes include the immediate (T1) and longer-term (T2) effect of the intervention on psychological distress, general emotional well-being, and coping self-efficacy. A within-trial economic evaluation will be conducted. Implementation outcomes will be assessed using mixed methods, according to the Reach, Effectiveness, Adoption, Implementation, and Maintenance (RE-AIM) framework. Data collection will include qualitative interviews and field notes. Discussion: It is anticipated that LISTEN will reduce diabetes distress among adults with diabetes. The pragmatic trial results will determine whether LISTEN is effective, cost-effective, and should be implemented at scale. Qualitative findings will be used to refine the intervention and implementation strategies as required. Trial registration: This trial has been registered with the Australian New Zealand Clinical Trials Registry (ACTRN: ACTRN12622000168752) on 1 February, 2022.