Working memory (WM) provides moment-by-moment information that is no longer physically present but relevant for a cognitive task. According to current task requirements, WM encodes new items, prioritizes items that become action targets or deprioritizes outdated or already used items. Since representations in WM are not independent of each other, such changes in task status might result in systematic inter-item biases. The most prominent bias is serial dependence where a previous item attracts a current item. It remains unclear under which task conditions serial dependence occurs. In two experiments, we asked participants to memorize the orientation of a briefly presented noisy grating of interest for a delayed report. Prior to its presentation, participants encoded two inducer gratings into WM. A retro-cue indicated that one of these inducer gratings had to be kept in WM. The other inducer grating was either used for a secondary judgment task but became irrelevant for the report (used but irrelevant inducer) or was not used for any other task (unused and irrelevant inducer). We found that the grating of interest was attractively biased towards the used but irrelevant inducer. In contrast, there was no serial dependence when the inducer was unused and irrelevant. Interestingly, the inducer remaining in WM repulsed the grating of interest. Our results showed that WM integrates a previous item into a current item only if the previous item was used for an action before losing its task-relevance. Thus, serial dependence in WM relies on action-related rather than stimulus-related representations.