Objective: Subjective well-being has well-established positive health consequences. During emerging adulthood, from ages 18 to 25 years, people’s global evaluations of their well-being (i.e., satisfaction with life [SWL]) appear to worsen more than any other time in the adult life span, indicating that this population would benefit from strategies to enhance SWL. In these studies, we investigated top-down (i.e., time-invariant, trait-like) and bottom-up (i.e., time-varying, state-like) influences of physical activity (PA) on daily SWL. Methods: Two daily diary studies lasting 8 days (N = 190) and 14 days (N = 63) were conducted with samples of emerging adults enrolled in college to evaluate relations between daily PA and SWL while controlling for established and plausible top-down and bottom-up influences on SWL. Results: In both studies, multilevel models indicated that people reported greater SWL on days when they were more active (a within-person, bottom-up effect). Top-down effects of PA were not significant in either study. These findings were robust when we controlled for competing top-down influences (e.g., sex, personality traits, self-esteem, body mass index, mental health symptoms, fatigue) and bottom-up influences (e.g., daily self-esteem, daily mental health symptoms, daily fatigue). Conclusions: We concluded that SWL was impacted by people’s daily PA rather than their trait level of PA over time. These findings extend evidence that PA is a health behavior with important consequences for daily well-being and should be considered when developing national policies to enhance SWL.