Eco-anxiety—emotional distress arising from awareness of environmental collapse—has become a critical dimension of social sustainability, linking mental well-being, professional functioning, institutional trust, and climate governance. This study investigates how higher education professionals (HEPs) experience and interpret eco-anxiety within their professional contexts, situating it as a lens on institutional legitimacy from the perspective of those who produce, teach, and steward climate knowledge. A cross-sectional mixed-methods survey of 556 HEPs was conducted across a month in 2023, combining an adapted climate anxiety scale with open-ended narratives. Quantitative analyses identified perceived governmental inadequacy as the strongest correlate of climate worry (β = 0.48, p < 0.001), accounting for 26% of the variance, whereas institutional inadequacy had a weaker effect. Qualitative findings revealed pervasive emotions of moral injury, solastalgia, and exhaustion when sustainability rhetoric outpaced genuine action, with many respondents describing governmental and institutional “betrayal.” Integrating Cognitive Appraisal Theory with concepts of moral legitimacy, the study conceptualises eco-anxiety as a relational and ethically grounded emotion reflecting the perceived misalignment between knowledge and governance. Addressing it requires transparent climate leadership, participatory governance, and organisational care infrastructures to sustain motivation and trust within universities. Eco-anxiety thus may function not only as a personal pathology but also as a psychosocial response that can illuminate HEPs’ perceptions of institutional misalignment with sustainability commitments, with implications for higher education’s contribution to the Sustainable Development Goals.