Physics First--a movement to invert the traditional science course sequence to teach physics at the ninth-grade level--is gaining interest. However, there is limited literature exploring how to support teachers in successfully implementing Physics First. To address this, a professional development (PD) program supporting a cadre of teacher-leaders was developed. Its impetus is to facilitate teacher-leaders in becoming advocates for excellence through developing their physics content knowledge and use of research-based pedagogy. The primary aim of this paper is to illustrate how Leadership in Freshman Physics, an NSF Math and Science Partnership (MSP), designed a leadership component to support high school physics teacher-leaders in a district-wide implementation of the Physics First curriculum. We describe lessons learned from our implementation and provide suggestions for future PD programs emphasizing teacher-leadership.