Visual working memory (VWM) capacity in humans is reached when individuals show an asymptotic activation level in the posterior parietal cortex, at around 3-4 items. We found that artificially increasing posterior parietal activity via positively-charged noninvasive anodal electric current, known as transcranial direct current stimulation (tDCS), can increase people’s VWM performance. This artificial improvement is more robust in low-capacity individuals who tend to remember less information. Event-related potential (ERP) comparisons between tDCS and sham conditions revealed that tDCS induced greater amplitudes in N2pc and sustained posterior contralateral negativity (SPCN), components that have been shown to reflect deployment of visual-spatial attention and maintenance of information in VWM, respectively. Together, these results suggest that VWM performance can be efficiently improved with external neural stimulation, which directly impacts the processes of visual attention and memory maintenance.