Facebook has frequently been implicated in Britain's 2016 EU referendum result, and support for leaving the EU has been linked to wider right-wing, right-wing populist and nativist movements which have found certain footholds online. However, limited qualitative sociological research has so far been conducted into support for Brexit, let alone its relationship to social media use. In particular, social media research focuses on big-data analysis; the question remains how and why individuals engage with pro-Leave and related right-wing, right-wing populist and nativist material online. There is also a dearth of research on the political social media use of 'non-digital-natives', the group statistically most likely to support Leave, and on research into Facebook, which is by far Britain's most popular social media platform. This project sought to understand how Facebook was used by non-digital-native Brexit supporters to engage with pro-Leave and related right-wing, right-wing populist and nativist content, and the significance of this engagement to their social and political lives. In doing so it aimed to shed light on the complex nexus between the recent phenomenon of support for Brexit, long-standing discontents with ethnic and religious diversity and liberal social change, and the evolving role of social media platforms in our political lives. The novel methodology for the study combined multiple semi-structured interviews with a cohort of 15 pro-Leave Facebook users, with one-month-long observations of their Facebook Wall activity. This allowed the study to take an interpretive approach that gave voice to participants' experiences, while simultaneously contextualising these in an immersive, ethnographic fashion. The findings reveal that the logic of the Facebook platform both afforded and encouraged participants to become politically engaged in ways that made them feel valuable and in control, within a socio-political context that they experienced as devaluing and disempowering. Elements of this logic found to play a role included Facebook's global connectivity, its algorithmically-driven automation, its emphasis on sharing, and its role as an alternative news provider. This combined with the crystallising issue of Brexit to mobilise existing grievances among participants. Participants accounted for their pro-Leave stances by avidly drawing on narrative templates provided by the content in their online milieus, and interpreting them in light of their lived experiences. These narratives cohered around a metanarrative that a global agenda exists that is deliberately facilitating or forcing 'left-wing' social change from above, to the detriment of 'normal' people like 'us'. This metanarrative conceived of power in similar ways to both conspiracy theories and populism, and employed frames of entitlement and demonisation that were culturally racist, nativist and Islamophobic. Finally, contrary to 'post-truth' claims that a shift towards privileging emotions over facts is behind Brexit and other contemporary mediated right-wing, right-wing populist and nativist phenomena, participants were extremely preoccupied with facts and demonstrating factful-ness. This was despite their experiences of, and narratives around, social media use also being highly emotive, reflecting the way in which emotions and rationality are not mutually exclusive. Overall, the thesis reveals that behind participants' use of social media was a desire to redefine claims to political knowledge while also reclaiming their own status as valued and empowered citizens, which was experienced as lost within an increasingly cosmopolitan and liberal society.