Collaboration among healthcare professionals has been widely cited as critical in ensuring optimal and efficient client care. To foster the development of this interprofessional competency in healthcare graduates, the University of Toronto created an Interprofessional Education (IPE) curriculum. However, the means by which the IPE curriculum developed interprofessional collaborative competencies in occupational therapy (OT) graduates had not been explored. The study identified the mechanisms and outcomes of University of Toronto’s IPE curriculum that contributed to OT graduates’ collaborative competency development. This study also identified the contexts in which this development occurred, and why such patterns were observed. This study employed a mixed-methods realist evaluation, which is an approach underpinned by program theories hypothesizing that specific contexts and mechanisms result in distinct outcomes. Qualitative and quantitative data from 2018 and 2019 OT graduates’ surveys, assessments, interviews, and reflection papers were utilized to test and refine initial program theories. Analysis revealed six outcomes that contributed to interprofessional collaboration: role clarification, team functioning, interprofessional communication, interprofessional conflict resolution, collaborative leadership, and advocacy. The analysis identified mechanisms that enabled and disabled the development of each outcome, and tested initial program theories, which aided refinement. The findings of this study can inform IPE curricula development, promote collaborative competency development in future OT graduates, and direct future IPE evaluation research