Purpose: This study investigated a teacher leadership program created by a partnership between a large US urban district, their teachers' union and a university. We were part of an action-research partnership that examined the program's implementation. Design/methodology/approach: We employed a hermeneutic phenomenology methodology and mixed-method data collection methods and analysis strategies to understand the experiences of program participants. Data included interviews with program participants, union leaders and district administrators along with an analysis of projects that participants created during the program. Findings: Teacher leadership programs were legitimized through diverse stakeholder collaboration, and involvement of a university partner was viewed as a value-add for teachers. Formalized teacher leadership programs professionalize teachers through expanding professional networks, developing leadership skills and lifting teachers' voices. When teacher leader work is directed towards school improvement, teachers' unique perspectives yield varied problems of practice and goals in ways that help schools address these problems. Practical implications: This study has implications for districts seeking to create teacher leadership opportunities and for districts and universities seeking to partner for in-service professional learning opportunities. Originality/value: This study underscores the role effective district-union-university partnerships can play in fostering pipelines for teacher leader development, which can better position school improvement efforts to be sustained over time.