Objective: To investigate directionality of the association between alcohol use and physical activity in a college student sample, longitudinally across three time points. Participants: A total of 396 undergraduate students from a large university in the United States (62% females) participated in this study. Methods: Self-report data of alcohol use and physical activity were collected at three timepoints with 3-month lags between waves. Random-intercept cross-lagged panel modeling was used to disentangle within- and between-person effects. Results: Despite no significant between-person effects, there were significant cross-lagged paths from alcohol use to vigorous physical activity at the within-person level. Specifically, when individuals consumed more alcohol than normal at earlier timepoints, they reported more subsequent vigorous physical activity at 3-month follow-ups. Conclusion: We provide evidence that alcohol use may positively predict later physical activity in college students over the course of a school year. These findings advance theoretical understanding of how these two health behaviors are linked using sophisticated methods.