Local implementation of science reform efforts in part relies on science teacher leaders (STLs) to improve science instruction in classrooms and beyond. The lack of science-specific professional learning resources drives STLs to act as boundary spanners to locate resources outside their local context to fill that gap. Museums and other informal science education centers are examples of external entities that STLs might leverage to locate resources for local science education improvement. While we know how museums support pre- and in-service science teachers, there is a gap in our understanding related to museum support for STLs. Here, we used case study research methods to analyze how a museum-based professional learning programme supported STLs, as boundary spanners to access and adapt resources for local science education reform efforts. We found that each STL reported benefiting from shared resources from the museum, as well as from their peers in their working groups. We also found that STLs reported on different elements of the professional learning programme related to their area of influence (classroom or district) and the problem of practice their group worked on. We discuss how each of the named features of the museum-based professional learning programme supported boundary spanning of STLs and end with implications and recommendations for the design of professional learning experiences to support their leadership work.