This study investigated the developmental impact of teacher autonomy support on changes in students' mental well-being and academic stress throughout upper secondary school. The sample consisted of 1453 Norwegian students (baseline M[subscript age] = 17.00; 60.6% girls; 80.9% Norwegian-born). The unconditional latent growth curve model results showed that perceived teacher autonomy support and mental well-being decreased during the three-year-long education. Academic stress, on the other hand, increased during this period. Findings from the parallel process latent growth curve model indicated that the initial status and change in teacher autonomy support were positively and negatively related to the initial levels and trajectories of mental well-being and academic stress, respectively. Girls experienced a higher level of academic stress and lower mental well-being and teacher autonomy support at the beginning of upper secondary school. Students with a higher socioeconomic status reported higher initial mental well-being and teacher autonomy support than others but also a more rapid decline in teacher autonomy support throughout upper secondary school. This study provides new insights into academic, psychological, and affective processes and their interrelationships during upper secondary school.