National human rights institutions have spread rapidly across Europe and its Neighbourhood consolidating their powers to protect human rights. Yet, we know little about the causes for change in the strength of national human rights institutions over time. We propose an analysis of institutional strength along two dimensions of safeguards – durability and enforcement – based on original data for 50 states. We illustrate the quantitative analysis with two case studies – Hungary and Poland. We find that European Union membership conditionality is the strongest predictor of increased strength in national human rights institutions. Additionally, we find evidence of democratic ‘lock-in’, as newly democratized states seek to increase the durability of their institutions. The influence of the United Nations and the European Union, through state networks, increases the strength of national human rights institutions, particularly their durability. The Council of Europe has a positive impact on the institutional safeguards for enforcement.