Metacognition is a well-researched construct important to successful learning. Recent studies show that state-level metacognition regarding self-control conflicts is also important for successfully resolving these conflicts. Because there exists no scale to assess trait-level metacognition in self-control and because of limitations of commonly used measures in self-control research, we adapted a scale that is widely used to assess trait-level metacognition in self-regulated learning, the Metacognitive Awareness Inventory (MAI). In two studies (N = 315 and N = 503), we constructed the 12-item Metacognition in Self-Control Scale (MISCS), which loaded on the two factors metacognitive knowledge and metacognitive regulation. The MISCS showed a good fit with good internal consistencies. In a 10-day experience sampling part of study 2, which included 9,639 reports of self-control conflicts, higher trait-levels of metacognition as measured with the MISCS predicted higher state-levels of success in resolving these conflicts, as well as higher state-levels of the subcomponents of metacognition, namely metacognitive knowledge, planning, monitoring, and evaluation. Most of these associations persisted when controlling for trait self-control, supporting the usefulness of the scale beyond the most commonly used scale in self-control research. The MISCS showed adequate test-retest reliability. Correlations with other scales, limitations, and future directions are discussed.