Need for Cognition (NFC) describes the relatively stable intrinsic motivation to engage in cognitive endeavors. Recent research has revealed the importance of NFC for affective adjustment, especially in combination with self-control. We followed up on those findings by addressing methodological issues as well as processes that may underlie relations of NFC to self-control. Study 1 (N = 102) examined whether NFC is associated with self-control independently of the measure or facet considered. Implicit willpower theories, that is, subjective beliefs concerning the limitation of self-control resources, were examined as a mediator for NFC predicting self-control. Higher NFC was associated with increased trait self-control but also with believing in unlimited self-control resources. The relation of NFC to willpower theories also mediated the prediction of trait self-control. Study 2 (N = 188) replicated relations of NFC to self-control. We further pursued the explanatory approach from Study 1 and experimentally manipulated willpower theories to provide insight into their association with NFC. Willpower theories were related to NFC but had no mediating role in predicting self-control. The experimental manipulation had no impact on situation-specific NFC. Altogether, both studies provided first evidence that relations of NFC to self-control depend on the self-control measure and that willpower theories may be crucial for explaining the association with self-control.