Participatory approaches can be seen as a requirement, but also as a benefit to the overall paradigm change towards sustainable development and contribute towards the integration of sustainability concept into the university culture. So far, there have been comparatively few research studies on participation within sustainability implementation at university level, and a more differentiated understanding of these processes is still missing, both in the practice of conducting a participatory process and in the sustainability assessment. This paper addresses some of the failures and successes experienced within participatory approaches in campus sustainability initiatives, and deduces a set of critical success factors and emergent clusters that can help to integrate the dimensions of participation more inclusively into sustainability assessment. Following a qualitative approach and inspired by the Delphi-method, semi-structured expert interviews (N = 15) and four focus group discussions (N = 36), with participants coming from twenty different countries in total, were conducted and compared according to qualitative content analysis. Findings give empirical evidence to some of the characteristics related to stakeholder engagement, and associate higher education for sustainable development to empowerment and capacity building, shifting away from a previous focus on environmental sustainability. The success of participatory approaches is interdependent with structural institutional conditions and the persons engaged, highlighting the importance of specific skills and participatory competencies. A better integration of the dimensions of participation into sustainability assessment practices can help in defining and establishing participatory approaches on institutional level and fostering a culture of participation in the transition to sustainable universities.