Seven studies including 488 patients with knee osteoarthritis were included in this systematic review and meta-analysis comparing transcranial direct current stimulation (tDCS) vs. sham stimulation. Pooled outcomes of interest included post-treatment and follow-up pain scores, Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), and Knee Injury and Osteoarthritis Outcome Score (KOOS). tDCS significantly improved post-treatment and follow-up pain scores (SMD = 1.03 and 0.83, respectively) and post-treatment WOMAC scores (SMD = 4.76), but no significant effect was observed on WOMAC scores at follow-up. These findings suggest tDCS may be effective for short-term pain relief and modest improvement in physical function in knee OA, though long-term benefits remain uncertain.