This cross-sectional study examined the predictive utility of the Multi-Process Action Control (M-PAC) framework for self-reported and device-measured physical activity behavior among a Hispanic-majority sample of adolescents. A total of 1849 high school students (Mean age = 16.0 ± 1.22 SD years; 52.3% female; 87.8% Hispanic) enrolled in one school district in South-central Texas completed a survey including instruments to assess M-PAC framework constructs and moderate-to-vigorous physical activity (MVPA) behavior. A subsample (n=435) wore accelerometers for seven days. Results from robust linear regression models revealed role identity and habit were significant predictors of self-reported MVPA. Role identity was a significant predictor of accelerometer-derived daily MVPA and raw acceleration in the most active hour, but not daily raw acceleration. Findings indicate reflexive processes are robust predictors of adolescent physical activity and should be the focus of interventions designed to promote adoption and maintenance of physical activity during this developmental life stage.