We aimed to compare the effect of transcranial direct current stimulation (tDCS) compared with sham or conventional interventions on motor functions and activity in individuals with Parkinson's disease. Two independent reviewers searched four databases (PubMed, Embase, Scopus, and Cochrane Library) from inception to April 2026. We only included randomized controlled trials comparing active tDCS (alone or with training) versus sham tDCS (alone or with training) on walking speed, functional mobility, Parkinson motor symptoms, activities of daily living, quality of life (QoL), dropouts, and adverse events. Two authors independently extracted data, including study source and design, participant and intervention characteristics, and outcomes. We computed a mean difference with a random-effects model. Subgroup analyses were performed for outcomes with greater than or equal to 10 experimental study arms, accounting for intervention protocol and stimulation site. We assessed the risk of bias using ROB 2 tool, and the certainty of evidence using Grading of Recommendations Assessment, Development, and Evaluation. Seventeen randomized controlled trials (n = 553) were included. Pooled analyses showed little to no effect on walking speed (mean difference: 0.04 m/s2, 95% confidence interval: -0.03 to 0.11), functional mobility (mean difference: 0.67 s gained on the Timed Up and Go test, 95% confidence interval: -0.64 to 2.02), and other outcomes. Subgroup analyses based on stimulation site and intervention protocol revealed no differences. Adverse events were minor and infrequent, and dropout rates did not differ between groups. The overall certainty of evidence ranged from very low to low. Current evidence suggests that the effect of tDCS on gait, activities of daily living, or quality of life is probably not superior to other conventional interventions in individuals with Parkinson's disease.