Emerging adulthood is an inherently stressful time characterized by instability and life change that may be linked to higher risk for depressive symptoms. Identifying potential mechanisms protecting from the effects of stress on depression may inform stress management programs targeting an understudied population of emerging adults. Physical activity (PA) may be a modifiable strategy aimed at reducing depressive symptoms emanating from periods of high stress. The purpose of this cross-sectional study was to explore PA as a moderator of the relationship between stress and depression among emerging adults. A total of 790 young adults participating in the Nicotone Dependence in Teens (NDIT) study provided self-report data on depressive symptoms, stressful life events experienced in the last year, and time spent in light, moderate, and vigorous intensity PA at age 20 (SD= 0.7 years). Based on regression analysis controlling for sex, age, and socioeconomic position, life stress (ÃŸ = 0.22, p< .01) was a significant predictor of depressive symptoms. Moderate intensity (but not light and vigorous intensity) PA moderated this relationship (ÃŸ = -0.08, p< .05), such that engagement in more moderate PA was associated with fewer depressive symptoms among individuals with high stress, while there was no association among individuals with low stress. These results provide continued evidence of the benefits of moderate-intensity PA in stress and mental health outcomes, and highlight the need to investigate different exercise intensities when exploring PA as a moderator of life stress.