Background: Diabetes mellitus requires ongoing management and care coordination. The majority of patients with diabetes were managed in primary healthcare settings. Several quality improvement programs have introduced specialist involvement in primary healthcare teams. However, synthesized evidence is needed to support policy improvements regarding the impact of specialist-primary healthcare coordination on glycemic control in diabetes care. Objective: This systematic review and meta-analysis aimed to assess the effectiveness of specialist involvement in primary healthcare teams on glycemic control of patients with diabetes. Methods: A search of five electronic databases (PubMed, Embase, Web of Science Core Collection, CNKI, and Wanfang Database) was conducted to identify relevant studies published until October 21st, 2023. We assessed the methodological quality of the included studies using the suggested risk of bias criteria for EPOC (Cochrane Effective Practice and Organization of Care). We conducted the certainty assessment using the GRADE guideline. The outcome measured was the HbA1c level. Meta-analyses were performed using random-effects models. Results: A total of 12 studies (7 randomized controlled trials and 5 controlled before-after studies) were included in the meta-analysis. The involvement of specialists in primary healthcare teams was associated with a statistically significant reduction in HbA1c level compared to usual or standard care (mean difference - 0.57, 95% CI: -0.86 to -0.27, I2 = 88.17%). Conclusion: The findings revealed that the interventions might improve the care delivered and patients' health outcomes. However, due to the very low certainty of evidence on the effectiveness on glycemic control, the interventions implemented in the included studies should be employed with caution in future policy-making to achieve improved HbA1c levels. Further research with a more rigorous design is needed to provide evidence of higher certainty and quality. Registration: The systematic review and meta-analysis was registered in the PROSPERO International Prospective Register of Systematic Reviews (registration No. CRD42022384589 available at https://www.crd.york.ac.uk/prospero/#searchadvanced ).