This study explored characteristics that principals, senior leadership team members, and middle leaders perceive as supporting the effective functioning of senior leadership teams (SLTs) in high-performing Catholic composite and secondary schools (CCSS) in Western Australia. Composite schools include both primary and secondary students. The study's research design was qualitative. The epistemology was constructivist, and the theoretical perspective was interpretivism (symbolic interactionism). The methodology used in this study was an instrumental case study. The research methods included one-to-one semi-structured interviews, focus group interviews, field notes and document search. The collected data were analysed, condensed and displayed, as results in matrix charts, following the cyclical model proposed by Miles et al. (2020). The results found that the characteristics principals, SLT members and middle leaders perceived as supporting the effective functioning of the SLT in high-performing composite and secondary schools were positive relationships, shared leadership, emotional intelligence, prioritising of vision and strategy, effective communication, availability to middle leaders, an improvement mindset and challenging events that provide a focal point for the SLT. A high performing Senior Leadership Team Framework was designed that synthesised insights from the literature review with results from this study.