Purpose: Compare leisure-time physical activity (LTPA) and active commuting to school among Brazilian adolescents between the periods before COVID-19 and after the reopening of schools. Methods: This is a repeated cross-sectional study with a nested cohort targeting high school students from Southern Brazil. LTPA and active commuting to school were the self-reported outcomes. Zero-inflated Gamma and Logistic Mixed models were applied to compare, respectively, LTPA and active commuting between survey years. Results: Cross-sectional analyses showed that the odds of engaging in any type of LTPA were similar between waves. However, active participants spent significantly more time in total LTPA (9.5 min/d), team sports (4.9 min/d), and fitness activities (7.7 min/d) in 2022 (n = 954; 52.0% female; 16.5 [1.2] y) than in 2019 (n = 824, 51.2% female; 16.4 [1.1] y). Prospective analyses of 286 adolescents (54.5% female) showed a reduction in the probabilities of engaging in total LTPA (−17%), team sports (−36%), and individual sports (−10%) from 2019 to 2022. No changes were found for active commuting. Conclusions: Cross-sectional and prospective differences were found for leisure but not for commuting-related physical activity between pre- and postpandemic periods. Efforts to promote physical activity should remain a public health priority.