Higher levels of sedentary behavior are associated with poor well-being, yet students sit for nearly 70% of their waking hours. Physical activity is an underexplored and emerging classroom tool that can be used to decrease students' classroom sedentary behaviour. This two-part investigation examined implementing "Fit-Breaks" during a 2-hour lecture on the well-being of university students, compared to a music control condition. "Fit-Breaks" are 10-minute bouts of easy-to-follow exercises and stretches that are designed to be safe and appropriate for students of all fitness levels within a resource and space-limiting environment. In both studies, lecture sections were randomly assigned to one of the conditions and students completed surveys on well-being at the start and end of the semester. Study 1 focused on global well-being, and study 2 honed in on dimensions of well-being. Based on a repeated measures ANOVA model and significance of p < 0.05, study 1 (N=162) demonstrated a significant interaction effect of break structure and well-being over time, F(1,160) = 5.66. In study 2 (N=380), a repeated-measures MANOVA showed a significant time effect, no group effect, and significant interaction effects across groups and psychological well-being over time for autonomy, F(1,378) = 5.34, p < 0.05 and personal growth, F(1,378) = 5.37, p < 0.05. These findings suggest that even small weekly bursts of physical activity in a real-world setting can positively improve well-being, with potentially strongest effects for autonomy and personal growth.