Background: Periodontitis is a chronic infectious–inflammatory pathology, with a high prevalence, which destroys the dental support and, if left untreated, leads to tooth loss. It is associated with other pathologies, particularly diabetes mellitus. Objectives: Our objective was to conduct a review of systematic reviews with meta-analyses to determine the evidence for periodontal treatment on periodontitis and diabetes. Second, we assessed the risk of bias and methodological quality using the AMSTAR-2 and ROBIS tools. Methods: We performed bibliographic searches in PubMed/Medline, Embase, Cochrane Central, Dentistry & Oral Sciences Source databases and in the Web of Science (WOS) scientific information service to identify systematic reviews with meta-analyses from the last five years. Results: Eighteen studies that met the inclusion criteria and evaluated 16,247 subjects were included. The most studied parameters were probing pocket depth, clinical attachment level, bleeding on probing and the glycated hemoglobin. Most of the included meta-analyses evaluated adult patients with periodontitis and type 2 diabetes mellitus (T2DM). Most of the meta-analyses considered and assessed by AMSTAR-2 showed significant methodological errors. The risk of bias was the domain with the worst assessment with the ROBIS tool. Conclusions: Despite the weaknesses of the included meta-analyses in terms of methodological quality and the risk of bias, periodontal treatment and DM treatment appear to contribute to improved clinical outcomes in a bidirectional manner between periodontitis and DM.