Background: This study aimed to examine cross-sectional and longitudinal associations between physical activity (PA), sedentary behavior (SB), and educational outcomes (EO) in first-year university students in Australia. Method: Participants (N = 80) engaged in 3 data collection points (semesters 1, 2, and 3) that included self-reported and device-based PA and SB, and objective EO measures. Cross-sectional associations were examined using linear and binary logistic regressions, and longitudinal associations were examined using generalized estimating equations. Result: Overall, results indicated some positive but weak cross-sectional associations between some device-based and self-reported measures of PA and EO outcomes when controlling for confounders. Self-reported SB was negatively associated with semester GPA at time point 3 after adjusting for confounders (β = −0.224; 95% confidence interval, −0.446 to −0.001; P < .05). No other significant cross-sectional or longitudinal associations were identified. Conclusion: Our findings suggest that SB may be a more important target healthy behavior than PA when aiming to influence EO, and that related interventions may be more appropriate in second rather than first-year university students. Further research is needed to better understand this relationship that uses larger sample sizes, follows students beyond first year, and includes measures that distinguish between leisure and educational screen time.