This thesis criticises G.A. Cohen's 'Karl Marx's theory of history: a defence' and the debate surrounding it, from the perspective of critical realism. It is a sustained critique of analytical Marxism's founding text and one of the first engagements of these two theoretical schools. It involves a close review of the basic terms of the book's presentation of a traditional conception of historical materialism and an assessment of Cohen's success in reconstructing a viable version of the theory. This is judged as a failure. Particular stress is laid upon the inapplicability of analytical philosophy to Marxism and Cohen's ambiguous relationship with the legacy of Hegel in Marx. His functionalist modes of explanation, the material-social division of reality, and the rational individual as a starting point for theory, are all found wanting. This criticism of static ahistorical models and the use of neo-classical methods, has, therefore, significant implications for the hole of the analytical Marxist project. Cohen's version of Marx's theory of history is shown to be unable to account for epochal transition - in particular the transition from feudalism to capitalism - and inadequate in dealing with the determination of the economy. The explanatory primacy of productive forces in history is rejected in favour of an alternative approach to agency, class and social structure. Further to this, a realist interpretation of the Marxist theory of value is offered, the place of class in historical materialism reviewed, and a partial reconceptualisation of relations and forces of production proposed.