Visual working memory (VWM) enables us to maintain visual information in service of upcoming goal-directed behavior. Previous research has shown that when an item in VWM is linked to a specific manual action, the brain prospectively prepares that action during the memory delay. Here we investigated whether such prospective action planning during VWM flexibly adapts to changing visual-motor mappings, occurs even when an upcoming action is only potentially relevant in multi-item VWM, and predicts subsequent memory-guided behavior. Human participants performed an orientation reproduction working memory task with one or two visual items while we recorded electroencephalography (EEG) and tracked contralateral attenuation of sensorimotor beta-band (15–25 Hz) activity as a neural marker of manual action planning. We found that early action encoding alongside VWM flexibly adapts to instructed task demands rather than reflecting rigid visual-motor mappings, occurs even for actions that are only potentially relevant to upcoming behavior, and predicts behavioral performance—leading to faster memory-guided responses for the prospectively planned item.