Charity sports events, specifically 5K events, reach large numbers of people and may help promote physical activity (PA). Few studies exist applying Self-Determination Theory (SDT) to participation in these events. This study examined changes in SDT constructs of Autonomy, Competence, and Relatedness satisfaction in participants (n = 207) of charity 5K events and (2) examined relationships among post-event SDT constructs, PA, and intention to complete future events. Participants completed online surveys before and after a charity 5K event using the Psychological Needs Satisfaction in Exercise Scale, Behavioral Regulation in Exercise Questionnaire-2, and International Physical Activity Questionnaire-Short Form. Repeated measures analysis of covariance analyzed the first purpose and regression the second. Competence satisfaction increased (