Stakeholder trust is central to advancing sustainable development, yet it is increasingly strained as corporate sustainability commitments expand faster than verifiable performance. This study examines how authenticity and transparency in corporate sustainability practices influence the formation and maintenance of stakeholder trust under conditions of scrutiny and institutional accountability. Using longitudinal evidence from European publicly listed firms and incorporating both comparative and contextual analytical perspectives, the research shows that trust grows when organizations communicate candidly, report measurable progress, and reinforce their commitments through credible assurance. Trust is shaped not by the volume of sustainability reporting but by the sincerity and consistency of alignment between commitment and demonstrable action. The findings highlight the role of institutional safeguards that encourage honest disclosure and responsible conduct as firms navigate sustainability transitions. This work advances the understanding of sustainable development governance by clarifying how credible communication and transparent practices can reinforce accountability and strengthen legitimacy. The insights offer practical direction for organizations and policymakers working to foster sustainability cultures grounded in integrity and long-term trust.