This study investigates the effect of whistleblowing on fraud prevention in the Nigerian public sector, focusing on whistleblowing systems, whistleblower protection, and organizational ethical climate. Drawing on agency and stakeholder theories, the study adopts a survey-based correlational design and collects data from 400 respondents across ministries, departments, and parastatals. The data were analyzed using multiple regression. The findings reveal that all three whistleblowing variables exert positive and significant effects on fraud prevention, highlighting the importance of accessible reporting mechanisms, protective frameworks, and supportive ethical environments. These results are consistent with prior empirical studies but extend the literature by providing evidence from Nigeria’s public sector, where research has been relatively scarce. The study concludes that strengthening whistleblowing mechanisms enhances transparency and accountability, and recommends reforms that improve reporting systems, enforce protections, and foster ethical organizational climates. In addition, the study recommends public sector leaders should cultivate cultures of fairness, trust, and psychological safety through ethical leadership training, fraud awareness programs, and recognition of employees who demonstrate integrity, thereby encouraging openness and disclosure.