This study investigated the impact of school-based mental health programmes on the adoption of sustainable lifestyles among Nigerian secondary school students. With environmental sustainability becoming increasingly important, fostering pro-environmental behaviors in youth is essential. Mental health has been identified as a key factor influencing decision-making, behaviors, and attitudes, including those related to sustainability. The study employed a quantitative research design using surveys to collect data from secondary school students in Nigeria. A total of 300 students from various schools participated in the study. The findings revealed that participation in mental health programs significantly influenced the adoption of sustainable lifestyle behaviours such as recycling, energy conservation, and waste management. The results suggest that these programmes foster emotional well-being, which in turn enhances students' capacity to make informed and responsible decisions regarding environmental issues. The study also found no significant impact of demographic variables such as gender and age on the relationship between mental health programmes and sustainable behaviours, suggesting that the impact of mental health education on sustainability is universal across these demographic factors. The findings emphasize the importance of integrating mental health education with sustainability initiatives in the school curriculum to promote both mental well-being and environmental responsibility. The study recommends among others that policymakers and educators should prioritise mental health programmes in secondary schools as a strategy for fostering sustainable lifestyles among students.