Major depressive disorder, commonly referred as "depression" in lay terms, has been one of the most prevalent psychiatric disorders worldwide. Approximately 1/5th of the population (with twice as many women affected as men) will experience this condition in mild, moderate, or severe forms throughout their lifetime. Despite the available treatment options, such as antidepressant medication and psychotherapy, it appears that in 20-30% of patients, the aforementioned therapy is ineffective, leaving these patients without further resources. Transcranial direct current stimulation (tDCS), a neurostimulation technique, could provide a possible solution to this problem. Several studies were conducted over the years, investigating the effect of tDCS, alone or in combination with pharmacological and/or psychological therapy, in treatment of depression. Unfortunately, these efforts have consistently yielded conflicting results with only limited effectiveness. Due to the wide variation in results, primarily attributable to significant differences in study design and tDCS protocols, it has been challenging to summarize the exact efficacy of tDCS. Future studies will need to adopt a uniform study design to enable comparability with other studies. This systematic review represents an initial effort to draw a generalized conclusion based on previously conducted studies, elucidating the extent to which tDCS, either alone or in combination with antidepressants and/or psychological therapy, can offer a solution in clinical practice for patients who do not respond adequately to standard treatment, which constitutes a large proportion of depressed patients. We also investigate the potential factors that may have influenced the obtained study results, thus providing a direction for further research in this area.