This thesis explores the role of mobility and displacement in shaping the development of English Catholicism from the beginnings of Henry VIII’s break with Rome, to the death of Mary I. The state-driven religious innovations of the 1530s and 1540s prompted over two hundred religious conservatives to flee England. This project examines how the experience of mobility re-shaped these emigres’ understandings of what it meant to be 'Catholic', catalysing the development of syncretic theologies and spiritualties that transcended both national and proto-confessional boundaries. It demonstrates how their peripatetic movements throughout Western Europe, combined with the material and emotional difficulties of displacement, encouraged the emigres to engage and experiment with new religious ideas they encountered abroad. This saw them connect with various localised manifestations of the Catholic Counter-Reformation, as well as with abortive efforts to heal the growing rift between the Catholic Church and its evangelical critics.

As well as deepening our understanding of the complex and sometimes seemingly contradictory ways in which mobility could shape religious identities, such conclusions have important implications for the contentious historiography of Mary I's reign. By demonstrating the extent to which repatriated emigres brought their experiences and encounters abroad to bear upon the Marian Church, this research not only connects Mary’s reign more fully with the historiography of the broader European Counter-Reformation – answering calls to ‘de-centre’ our approach to Catholic reform in this period – but it also challenges recent interpretations of Marian Catholicism as remarkably confessionalised. It highlights instead the considerable disagreements that developed between former emigres and their compatriots about the direction Catholicism should take under England’s first queen. This thesis argues that recognising this schizophrenia at the heart of the Marian Church not only helps explain why the historiography of her reign continues to be so divergent, but also changes our understanding of that reign's place within the wider history of the Reformation in England. Far from an 'interlude' as it has long been regarded, Mary's reign needs to be recognised as a central point around which the Reformation as a whole pivoted and which set the precedents for much of what was to follow.