Evolving conceptions of the purposes of higher education suggest the need for assessment practices that contribute to preparing students to navigate complex social-ecological challenges. Though shifts in assessment discourse have begun to respond to this need, further examination of the role of students in assessment processes is required. One strategy that has been highlighted is rubric co-design, in which students and instructors interactively deliberate assessment criteria. However, the literature shows that student voices are typically limited in these processes. To address this gap, this study advances a student-led rubric co-design process to promote student agency and learning. Principles from sustainability are applied to orient the activities of students in this approach by emphasizing the participative, normative and integrative features of the process. A formative intervention was conducted in an undergraduate course focused on professional skill development. Data were collected through individual and group reflections, with reflexive thematic analysis applied to develop themes that represented the ways that students navigated their experiences in the assessment process. Findings demonstrate the promise of the approach in enhancing student agency and promoting self-formation as emerging professionals, while articulating the phases and strategies that shape students’ leading role in rubric co-design processes.