Drawing on their experience of mental health social work in Northern Ireland and the Republic of Ireland, the authors examine the impact of current legislative and policy change in both jurisdictions. The paper applies Lorenz’s theoretical framework to develop a comparative analysis of how global and country specific variables have interacted in shaping mental health social work. The analysis identifies linkages between factors and indicates similarities and differences in mental health social work practice. The paper highlights emerging discourses in this field and explores the impact on practice of developments such as de-institutionalisation, community care, and ‘user rights’ versus ‘public protection’. The article concludes with a review of key challenges facing social workers in both jurisdictions and identifies opportunities for developing mental health social work in ways that can positively respond to change and effectively address the needs of mental health service users and their carers. The analysis provides an opportunity to evaluate Lorenz’s theoretical framework and the paper includes a brief critical commentary on its utility as a conceptual tool in comparative social work.