Cardiometabolic diseases share many modifiable risk factors. However, periodontitis, a chronic inflammatory condition of the gums, is a risk factor that is rarely publicized. This systematic review aims to evaluate the impact of oral hygiene practices on the risk, incidence, and/or mortality rate of cardiovascular disease (CVD), type 2 diabetes mellitus (T2DM), and chronic kidney disease (CKD). Searches were conducted using MEDLINE, Embase, Scopus, and CINHAL. Randomized controlled trials (RCTs), quasi-RCTs, and observational studies were included. Eligible studies reported on associations of toothbrushing, interdental cleaning, mouthwash, or toothpaste use, either alone or in combination with CVD, CKD, and/or T2DM outcomes in adults ≥ 18 years. Fifty-five studies were included. Cochrane’s risk of bias tool and the Newcastle–Ottawa Scale were used for quality assessment. Data synthesis is narratively presented. Toothbrushing and interdental cleaning were associated with lower risk of developing T2DM or hypertension HR 0.54 [p < 0.001] and a lower mortality risk in those with CVD HR = 0.25 [p = 0.03]. Mouthwash use reportedly increased the risk of developing hypertension and diabetes by 85% and 55%, respectively. This review highlights how simple oral hygiene practices can reduce cardiometabolic risk. Non-dental clinicians could integrate the findings into chronic disease health promotion.