Transcranial direct current stimulation (tDCS) is a non-invasive brain stimulation technique that has grown in popularity over the past two decades as an alternative treatment option for various neuropsychiatric disorders. tDCS modulates cortical excitability through the application of a weak direct current to the scalp via electrodes placed over cortical regions of interest. It has been shown to be a promising and relatively safe treatment tool with few adverse events. In this article, we will briefly review the efficacy of tDCS in depression, bipolar disorder, schizophrenia, and obsessive-compulsive disorder. We will also discuss biomarkers of tDCS efficacy in depression, as it is the most studied neuropsychiatric disorder using tDCS application. We will then offer suggestions for future directions. Although efficacy results show promise, more studies with larger samples and longer treatment periods are needed to better understand the benefits of using tDCS as an alternative treatment option for neuropsychiatric disorders.