Purpose: To summarise the available data on the effects of chlorhexidine (CHX) mouthwash in treating gingivitis during treatment with fixed orthodontic appliances. Materials and Methods: Multiple electronic databases were searched up to December 7th, 2021. Only randomised controlled trials (RCTs) were eligible for inclusion. The quality of the included RCTs was assessed with the Cochrane risk of bias tool for randomised trials (RoB 2.0). After data extraction and risk of bias assessment, differences were recorded in several oral hygiene indices in time and mean percentage change in those indices using different antimicrobial solutions. Results: Fourteen studies were deemed eligible for inclusion, reporting on a total of 602 patients with an age range of 11–35 years. The experimental solution was a 0.06%, 0.12%, or 0.2% CHX mouthwash with the control either a placebo mouthwash or a selection from a variety of mouthwashes. Treatment duration varied from 1 day to almost 5 months and the follow-up period varied from 1 min to 5 months. Chlorhexidine mouthrinses led to reduced plaque accumulation and gingival inflammation during orthodontic treatment, while at the same time, some of the control group mouthrinses were deemed equally effective. No statistically significant difference was detected in the meta-analysis between CHX and mouthwashes with propolis/probiotics/herbs in terms of the gingival index at 3 to 4 weeks (mean difference 0.07, 95% CI: -0.18, 0.31, p = 0.59). Conclusion: Chlorhexidine mouthwash in orthodontic patients successfully controls gingival inflammation and bleeding when compared to untreated controls, but is equally effective as other mouthrinses where various oral health indices are concerned.