Background: There is consistency of evidence on the link between school culture and student health. A positive school culture has been associated with positive child and youth development, effective risk prevention and health promotion efforts, with extensive evidence for the impact on student mental health. Interventions which focus on socio-cultural elements of school life, and which involve students actively in the process, are increasingly understood to be important for student mental health promotion. This qualitative study was undertaken in three UK secondary schools prior to the implementation of a participative action research study bringing students and staff together to identify changes to school culture that might impact student mental health. The aim was to identify how school culture is conceptualised by students, parents and staff in three UK secondary schools. A secondary aim was to explore which components of school culture were perceived to be most important for student mental health. Methods: Across three schools, 27 staff and seven parents participated in in-depth interviews, and 28 students participated in four focus groups. The Framework Method of thematic analysis was applied. Results: Respondents identified elements of school culture that aligned into four dimensions; structure and context, organisational and academic, community, and safety and support. There was strong evidence of the interdependence of the four dimensions in shaping the culture of a school. Conclusions: School staff who seek to shape and improve school culture as a means of promoting student mental health may have better results if this interdependence is acknowledged, and improvements are addressed across all four dimensions.