Objective To analyse the effectiveness of exercise therapy in improving pain and active or passive maximum mouth opening in patients with temporomandibular disorders. Data sources PubMed Medline, Web of Science, Scopus, CINAHL Complete and Physiotherapy Evidence Database, until April 2022, in accordance with Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Review methods We included randomized controlled trials evaluating the effect of exercise therapy on pain and on active and passive maximum mouth opening in patients with temporomandibular disorders. Effect size was calculated using Cohen's standardized mean difference (SMD) and their 95% confidence interval (95% CI) in a random-effects model. Results A total of 16 studies with 812 participants were included. Exercise therapy is effective in reducing pain (SMD: −0.58; 95% CI: −1.01 to −0.12) and increasing the pain pressure threshold (SMD: 0.45; 95% CI: 0.14–0.76), active and passive maximum mouth opening (SMD: 0.43; 95% CI: 0.14–0.71 and SMD: 0.4; 95% CI: 0.06–0.75, respectively). Subgroup analyses showed more effect of exercise therapy more splints versus splints on pain (SMD: −0.5; 95% CI: −0.73 to −0.26), active and passive maximum mouth opening (SMD: 1.14; 95% CI: 0.22–2.07 and SMD: 0.56; 95% CI: 0.06–1.06, respectively). On pain pressure threshold, exercise therapy was better than physiotherapy approach (manual therapy and electrotherapy) (SMD: 0.48; 95% CI: 0.09–0.87). Conclusions Therapeutic exercise is an effective therapy to reduce pain and increase pain pressure threshold and active and passive maximum mouth opening in patients with temporomandibular disorders.