Internationally, science, technology, engineering, mathematics (iSTEM) education continues to flourish in schools, with many now embracing the combined disciplinary assumption suggested by its acronym; integrated STEM (iSTEM) education. Advocated for its potential to increase student interest and achievement in STEM subjects, courses, and careers, leadership in iSTEM education is beneficial for promoting its success in schools. However, there is limited understanding of the characteristics of effective iSTEM teacher leaders. Seeking to provide greater insight into iSTEM teacher leadership, the research question addressed in this study is: What are the characteristics of iSTEM teacher leaders? This qualitative study explored teacher leaders' perceptions of the characteristics valuable for supporting iSTEM education in schools. Data collected involved semi-structured interviews with five teachers implementing and leading iSTEM education. Findings identify the importance of iSTEM education-specific characteristics such as disciplinary knowledge and creating iSTEM teaching resources. Differences between leaders revealed the importance of considering contextual needs and capabilities. This paper discusses the identified characteristics and their importance in supporting iSTEM progression in schools, providing valuable insight for school principals and those designing leadership programs for teachers, as well as suggestions for further research.