This thesis explores the lived experiences of Irish male migrants who came to London during and after World War Two to work as builders in the construction and civil engineering industries. Using extensive primary, archival and secondary sources, this research blends socioeconomic, construction and cultural history to compare and contrast a wide range of cultural representations disseminated about these workers through Irish public discourse, culture and folklore. Twenty-one original oral histories collected for this project are a crucial part of the primary research, supported by an array of corroborative journalistic and corporate documentation. This research concludes that these representations focus too narrowly upon a range of negative stereotypes, connotations and socio-economic outcomes. Contrary to these representations a significant majority of post-war migrants – whilst struggling through the inevitable hardships of immigration - eventually led (or lead) productive, moderate, happy, socio-economically viable, stable and rewarding lives in London. This is the first research to make an objective evidence-based empirical survey, in quantitative and qualitative terms, of the cohort of Irish migrants who worked on the post-war reconstruction of London. It is also the first research to establish the geographic, socioeconomic and cultural patterns to their migration stories and to link those patterns to underlying theoretical concepts. An example is the synthesis of theoretical ideas relating to social capital, networking, cultural circuits and ethnic entrepreneurship. This posits that Irish migrant construction workers generally operated within an ‘auto-segregated’ workspace and socialised within a volitional self-enclosed community. This community exhibited characteristics of both ethnic and diasporic enclaves and gradually developed a form of niche ethnic economy. Other novel aspects of this work are: the granular analysis of the casualised recruitment system known as ‘the lump’ and the performative masculinities it elicited; the crucial role played – albeit surreptitiously – by women in the Irish migrant construction environment; the detailed histories of key Irish-founded British construction firms; and the elucidation of how their entrepreneurial success fed back into developments in Irish political and economic life in the post-war decades. The hope is that this research ignites further and deeper historical interest in the histories of the people who created the metropolitan centres of the world, rather than simply the structures of the cities themselves.