Knowing what one knows and accurately monitoring one's own capacities and performance on a moment-to-moment basis are important determinants of task success. Individual differences in such metacognitive monitoring are well documented, but what determines an individual's monitoring accuracy in a particular context is yet to be fully understood. One candidate contributor to monitoring accuracy is working memory. In this study, we investigated whether and how working memory contributes to the accuracy of monitoring processes. Most evidence for a positive relationship between working memory and monitoring accuracy has been provided by correlational studies. Here, an experimental approach was applied in which confidence judgments were collected after each memory recall in three working memory experiments, and the effect of increasing the working memory demands on monitoring accuracy was examined. A visuospatial complex span task, a verbal complex span task, and an updating task served as the working memory tasks, to cover the range of methods used in working memory research. Confirmatory analyses conducted using cumulative link mixed models indicated that in two out of three experiments, monitoring accuracy suffered when working memory demands increased. As such, the weight of evidence supports a dependent relationship between working memory and monitoring processes, whereby monitoring accuracy can fluctuate during a task depending on the available cognitive resources. This indicates that the sensitivity of metacognitive monitoring is at least partly determined by the nature of the cognitive processing taking place in the primary task.