This study examined basic psychological need satisfactions for competence, autonomy, and social relatedness in physical education (PE) and their contributions to accelerometer-based in-class and total moderate to vigorous physical activity (MVPA) across a one-year follow-up (T1). Participants were 523 students (girls 280, boys 243; mean age = 11.26 ± 0.31) and the data were collected using self-reports and waist-worn accelerometers. The key findings were: (a) competence and social relatedness need satisfaction at baseline (T0) predicted total MVPA at T1 via total MVPA at T0; (b) in-class MVPA at T0 predicted total MVPA at T1 via total MVPA at T0; (c) in-class MVPA was directly associated with total MVPA at T0 and T1; and (d) boys scored higher than girls on competence and relatedness need satisfaction at T0. These findings indicate that the need satisfactions for competence and social relatedness in PE are central components facilitating the greatest increases in total MVPA participation. To improve student outcomes, it is essential that all children receive positive and satisfying PE experiences. Enhancing the readiness and capability of pre- and in-service teachers through teacher training programmes is vital to raising awareness of the basic psychological need satisfactions behind autonomous motivation and greater MVPA engagement.