Whistleblowing is an important prosocial activity, one which facilitates the early detection and correction of misconduct and deters future misconduct. Recognizing this, many governments have signalled its legitimation by enacting legal protections for public sector whistleblowers, including in the Westminster governments of the United Kingdom, Canada, and Australia. The success of whistleblowing regimes in these jurisdictions is contested, however, as mismanaged programs and retaliation against whistleblowers continue to make headlines. This presents a conundrum. Previous studies have established that if failures accumulate and visible successes are few, employees will lose trust in the regime and use it less, if at all. This would constitute a public policy failure and undermine the implicit long-term goal of improved governance. Departing from previous research approaches, this dissertation uses historical and rational choice institutional theory to test the hypothesis that whistleblowing regimes are born of crisis, but the extent to which they are effectively implemented is dependent on ongoing bureaucratic and political support. This support is contingent upon the regime being consistent with existing institutional arrangements and incentives. When it is not, dysfunctional responses to whistleblowing will continue. Three case studies are presented in order of regime enactment, with the United Kingdom in 1998, Canada in 2005, and Australia in 2013. Process tracing was used to examine three embedded units of analysis: pre-regime institutional development, whistleblowing regime implementation, and the factors effecting regime performance. The findings partially confirm the hypothesis. The whistleblowing regimes followed a similar pattern, but there were two triggers for whistleblowing legislation - punctuated equilibrium after a crisis, or isomorphism to boost legitimacy, driven by political exigencies. Support is fleeting, moreover, as political actors quickly shift their attention to different priorities. Administrative actors adopt several strategies to resist the regimes, including shaping them to be less threatening, unenthusiastic enforcement, and continued reprisals. Although the regimes do conform to Westminster conventions and norms, these have been eroded as political actors have intruded into administration and taken control of incentives. These favour responsiveness to political direction and the suppression of bad news, undermining the intent and performance of the whistleblowing regimes.