Purpose: This research aims to investigate the role of project-based-learning within graduate sustainability curricula through the lens of key competence development. Project-based learning has become a widely recommended pedagogy for sustainability education. It is hypothesized that through collaboration, student autonomy and real-world application, students develop key competencies for sustainability. This paper also aims to examine the connection between project-based learning and competence development on a program level from the student perspective. Design/methodology/approach: This two-year comparative case study follows the project-based-learning journeys of nine graduate sustainability students from three programs: the Master’s of Sustainability at Arizona State University, the Master’s of Sustainability Science at Leuphana University of Lüneburg and the Global Sustainability Science Master’s, an ASU and Leuphana collaboration. Over four semesters, the students each took part in four competence-oriented self-assessments and interviews to map their perceived learning throughout their programs. Additional contextual information was gathered from program and course materials and descriptions, instructor interviews and in vivo observations. Findings: The defining aspects of project-based learning including collaboration, student autonomy and real-world connection do contribute to students’ self-perceived competence development. Student-driven and program-driven project-based learning experiences equally foster this result, as long as the pedagogical challenges of balancing support and student independence associated with each are mitigated through instructor actions, program design or individual student coping skills. Originality/value: The results of this research can support higher education institutions in designing sustainability programs aimed at competence development through project-based learning. The focus on the curricular and program level combined with repeated overtime student-reported attribution to specific courses and activities bridges the gap between individual course case studies and theoretical recommendations for curriculum design. In addition to length and depth, this study also forefronts student experience of curricula as delivered.