Barrett McMahon was born in Limerick and read history at University College Cork before spending a decade working in archival research across Lisbon, Porto, and Rio de Janeiro. His interest in the Atlantic dimensions of Irish and Iberian history developed from a long fascination with the parallel constitutional crises that shook the western European periphery in the early nineteenth century. He has written extensively on Irish, Portuguese, and Brazilian historical subjects, and his narrative approach draws on primary sources from multiple national archives to recover the human texture of political transformation. He lives in County Clare, where he continues to write on the history of constitutionalism, empire, and the making of the modern Atlantic world.