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 (ie, 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 (ie, time-invariant, trait-like) and bottom-up (ie, time-varying, state-like) influences of physical activity (PA) on daily SWL. 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. 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 (eg, sex, personality traits, self-esteem, body mass index, mental health symptoms, fatigue) and bottom-up influences (eg, daily self-esteem, daily mental health symptoms, daily fatigue). 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.