Purpose The purpose of the study was to evaluate the effectiveness of a peer leader-led (PL) diabetes self-management support (DSMS) group in achieving and maintaining improvements in A1C, self-monitoring of blood glucose (SMBG), and diabetes distress in individuals with diabetes. Diabetes self-management support is critical; however, effective, sustainable support models are scarce. Methods The study was a cluster randomized controlled trial of 221 people with diabetes from 6 primary care practices. Practices and eligible participants (mean age: 63.0 years, 63.8% female, 96.8% white, 28.5% at or below poverty level, 32.5% using insulin, A1C ≥7%: 54.2%) were randomized to diabetes self-management education (DSME) + PL DSMS (n = 119) or to enhanced usual care (EUC) (DSME + traditional DSMS with no PL; n = 102). Data were collected at baseline, after DSME (6 weeks), after DSMS (6 months), and after telephonic DSMS (12 months). Results Decreases in A1C occurred between baseline and post-DSME in both groups. Both groups sustained improvements during DSMS, but A1C levels increased during telephonic DSMS. Improvements in self-monitoring of blood glucose were observed in both groups following DSME and were sustained throughout. At study end, the intervention group was 4.3 times less likely to have diabetes regimen-related distress compared to EUC. Conclusions PL DSMS is as effective as traditional DSMS in helping participants to maintain glycemic control and self-monitoring of blood glucose (SMBG) and more effective at improving distress. With increasing diabetes prevalence and shortage of diabetes educators, it is important to integrate and use low-cost interventions in high-risk communities that build on available resources.