Terence O’Neill maintained a keen interest in conservation and architectural heritage, but his record on these issues in government in Northern Ireland is largely unexamined. This article addresses this deficit through a comprehensive review of the existing literature reinforced by archival material, revealing the familial and other connections that O’Neill had with the conservation world and civil society organisations, including his sometimes behind-the-scenes interventions on conservation policy. The momentous impact on the existing built environment from his drive to ‘transform the face of Ulster’ is ultimately foregrounded, particularly the contemporary philosophy underpinning the ‘balanced approach’ to development that was initially favoured by progressive opinion in the early 1960s, and the effect that the destruction of familiar places had on the creation of new heritage values. However, the failure of O’Neill to introduce town and country planning legalisation akin to that existing in Great Britain frustrated the efforts of conservationists who grew increasingly vociferous in their calls for action. As in other contested areas of public policy in the 1960s in Northern Ireland, the destructive forces unleashed in the built environment threatened architectural heritage and essentially remained unchecked in the absence of timely reforms prior to Direct Rule from Westminster.