Thirteen randomized controlled trials including 540 patients with knee osteoarthritis were included in this systematic review and meta-analysis comparing transcranial direct current stimulation (tDCS) vs. sham tDCS. Pooled outcomes of interest included pain, physical function, stiffness, mobility performance, quality of life, pressure pain tolerance, and plasma levels of brain-derived neurotrophic factor (BDNF). Pooled results indicated a significant decrease in pain with tDCS, but no significant improvements in physical function, stiffness, mobility performance, quality of life, or pressure pain tolerance. There was a significant reduction in plasma levels of BDNF. The main findings suggest that while tDCS can alleviate pain in patients with knee osteoarthritis, it may not improve other clinical outcomes.