In recent decades, European Union (EU) enlargement has substantially altered the continent’s economic and political landscape by lowering barriers to trade, labor mobility, and capital flows. Migration emerges as a central factor in this transformation, especially following the accession of Central and Eastern European countries. This enlargement has intensified interest among policymakers and researchers in the factors driving intra-European migration and its economic and social implications.

This study specifically investigates the interplay between EU enlargement, the Freedom of Movement (FOM) agreements, and Brexit on labor mobility. Although EU enlargement has generally been associated with deeper economic and political integration, its most profound impact may lie in facilitating international migration. By distinguishing between the timing and impact of EU membership and the Freedom of Movement (FOM) agreements—often introduced at different times— the analysis provides a nuanced view of their respective roles.

Employing a gravity model framework with Poisson Pseudo-Maximum Likelihood (PPML) estimation and a heterogeneity-robust difference-in-differences (DiD) approach, this study examines bilateral migration flows across 224 origin-destination country pairs. The results reveal that EU membership significantly increases migration flows, particularly from newer to older member states, indicating a pronounced east-to-west asymmetry. This effect remains robust after accounting for FOM implementation, and further robustness checks confirm the consistency of the findings under different policy timelines and the inclusion of external mobility agreements.

Additionally, the study explores the impact of Brexit on return migration, uncovering a substantial rise in flows from the UK to EU member countries—especially those that joined after 2000—following the 2016 referendum. These patterns highlight the heterogeneous and asymmetric effects of different EU migration policies and suggest that Brexit exerts a stronger influence on return migration than FOM.

Consequently, the findings highlight the importance of policy-specific analysis in capturing the complexities of migration responses to institutional changes within the EU.