This thesis responds to a question Alexander Weheliye poses in Habeas Viscus: ‘what different modalities of the human come to light if we do not take the liberal humanist figure of Man as the master-subject but focus on how humanity has been imagined and lived by those subjects excluded from this domain?’. Concentrating on fiction published in Britain between 1950 and 1980, a point in history in which that ‘master-subject’ comes under scrutiny and under pressure, this thesis reads mid-century literature through the lens of the posthuman. In doing so, the chapters that follow offer a fresh perspective on texts by Angela Carter, Barbara Comyns, Kamala Markandaya, Barbara Pym, and Muriel Spark, developing an approach to reading those texts that embraces the diversity of form and style in post-war fiction. This approach draws on posthuman and posthuman adjacent theory to show how mid-century literature critiques what Weheliye calls the master-subject and what I call the Human, a hierarchical way of organising the world predicated on bounded, agential subjectivity. Anticipating what is now termed critical posthumanism, British post-war fiction makes connections between acts of violence and the hierarchical Human to link racism and misogyny in post-war society with the dominance of Weheliye’s master-subject. Going beyond that systemic critique, the texts I focus on in this thesis also explore other ways of being and knowing. Invoking a fluid poetics that turns improbable and impossible bodies into posthuman ‘bodyings’, these novels invite attention to a mutable, affective ontology ‘outside the world of Man’