This study explored cross-sectional associations between prior weight stigma experiences, physical activity (PA) intentions, behaviors, and the acute effects of a weight stigma exposure on PA intentions and behaviors among undergraduate students. Weight-stigma experiences and behavioral intentions were self-reported. Moderate-to-vigorous PA and total PA were assessed using accelerometry. Participants were randomized into two experimental conditions (a weight stigma or control condition) to assess the acute effects of a weight stigma exposure. Forty-nine students (81.6% female; 59.2% Non-Hispanic White; 19.6 ± 1.1 years of age; body mass index: 23.9 ± 4.0 kg/m[superscript 2]) completed the study. Prior weight stigma experiences were positively associated with PA avoidance ([beta] = 12.1 ± 2.7; p < 0.001) but were not associated with positive PA intentions or behaviors (ps > 0.05). There were no differences in positive PA intentions, PA avoidance, or PA behaviors across conditions (all ps > 0.05). Future studies should examine the long-term effects of weight stigma on PA avoidance and objectively measured PA in young college students.