Purpose: This study aims to examine the mediating role of students' knowledge of sustainable development (SD) in the relationship between green campus initiatives by higher education institutions (HEIs) and student proactivity. Design/methodology/approach: The research, with a quantitative approach, was carried out with students linked to HEIs belonging to the Sustainable Campus Network - Portugal (RCS-PT). Findings: It was concluded that communications of HEI SD initiatives, green campus operations and approach to SD in the classroom have a positive and significant effect on students' proactivity toward SD. It was also concluded that SD-oriented student knowledge is a mediator in these relationships. Research limitations/implications: An underlying argument is that students with SD-oriented knowledge engage in proactive behaviors, taking the best HEI initiatives as a precedent among students of the HEIs belonging to the RCS-PT. Practical implications: HEI initiatives can be drivers for proactive student behaviors regarding SD. Thus, this study brings guidance to university leaders and other stakeholders. The findings can also be useful for those involved in planning SD-oriented actions in HEIs. Social implications: Strengthen the role of higher education as co-creators of change by promoting the principles of SD in future professionals. Education is a strong instrument for behavioral change, so HEIs play a fundamental role here having a direct impact on society. Originality/value: This research sought to expand the dialogue about SD in HEIs, especially in achieving sustainable development goals, intertwined with the idea of participation and engagement of students.