Despite a need for strong K-12 STEM education globally, professional development systems for STEM teachers in the United States lack coherence or sequenced experiences to recruit, develop, and retain master teachers and teacher leaders in STEM. Still, the United States produces erudite STEM master teachers and effective STEM teacher leaders, which asks the question to how, where, and when these teachers sought out opportunities to develop their teaching competencies and hone their leadership skills to become STEM master teacher leaders. Using an interpretive phenomenological approach, framed by master teacher leadership development, this study examined the lived experience of 10 nationally recognised STEM teacher leaders: Presidential Awards for Excellence in Mathematics and Science Teaching awardees and/or alumni of the Albert Einstein Distinguished Educator Fellowship Program. Participants provided detailed accounts, identifying and scrutinising key experiences in their teaching career that led them to national recognition as an STEM master teacher leader. Five themes emerged from the interpretive phenomenological analysis: the importance of school culture and STEM community, access to professional networks/opportunities, motivation, luck, and reinforcing beliefs. These themes, aligned with international exemplars of teacher professional development pathways, suggest areas of improvement for STEM master teacher leadership within the United States.