The objective of this study was to examine the role of basic psychological need satisfaction as a potential mediator of the relationship between health-enhancing physical activity (HEPA) and well-being. Participants (N = 201) were young adults who recalled their HEPA behavior, experiences of psychological need satisfaction, and levels of well-being across multiple indicators using a cross-sectional design targeting the previous day. Results from path analysis demonstrated that effort put forth in HEPA activities, as opposed to frequency or duration of HEPA, predicted well-being. Further, psychological needs satisfaction mediated between 10% and 44% of the HEPA-Effort – well-being relationship. Overall, these findings lend credence to the notion that effortful investment is associated with well-being when engaged in HEPA, and that the satisfaction of basic psychological needs may act as a salient explanatory mechanism partially accounting for that relationship.