This research sought to test whether sport participation relates to the development of trait extraversion across three life phases. Sport participation and extraversion were measured in children aged 10.5 ± 0.5 years (n = 3600), in adolescents aged 14.5 ± 0.5 years (n = 3463), and in adults with a mean age of 49.4 ± 18.0 years (n = 12,280), with corresponding data collected four years earlier. There were small mean-level decreases in extraversion during childhood and adulthood, and a large decrease in extraversion during adolescence. Four-year rank-order stability in extraversion was.58 in childhood,.61 in adolescence and.76 in adulthood. Sport participation was associated with higher extraversion in all three samples. After controlling for sociodemographic factors, children and adolescents who dropped out of sport showed greater decreases in extraversion than those who continued participation in sport. Sport participation was unrelated to mean-level change in extraversion during adulthood. Sport participation was also associated with greater intra-individual stability in extraversion for children, adolescents and adults. There were no significant sex moderation effects for mean-level change or individual-level stability. These findings provide evidence that sport participation might have an important role in trait extraversion stability and change across the lifespan.