This thesis examines the development of Georg Lukacs's early philosophy, and specifically of his concept of the subject-object dialectic, from the History of Development of Modern Drama (1908) to History and Class Consciousness (1923). Between 1908 and 1918, Lukacs came to see as the only possible philosophical options either Hegel's ontology or a resolutely anti-ontological Neo-Kantian value-philosophy inspired by Lask, combined with a quasi-religious metaphysic inspired by Fichte, Kierkegaard and Dostoevsky. In the Heidelberg Aesthetics (1916-1918), the programme of Hegel's metaphysics (the phenomenology of the identical subject-object) is presented as only realizable within a resolutely non-metaphysical aesthetic, as one sphere of validity within a Neo-Kantian framework. History and Class Consciousness transposes the logical structure of this aesthetic theory into the ontological domain, articulating a Marxist critique of Neo-Kantianism which rediscovers in the proletariat the phenomenology of the identical subject-object as the logic of being, i.e. as ontology. This thesis is the first study in English to bring to light fully this dialectic, because it is the first to analyze Lukacs's Philosophy of Art (1912-1914) and Heidelberg Aesthetics (1916-1918), and their relation to History and Class Consciousness. It contributes not only to a new understanding of Lukacs's transition to Marxism, but also sheds light on the genesis of his later philosophy. Its detailed critique of History and Class Consciousness from a point of view inspired by the dialectics of labour in Lukacs's later Ontology of Social Being, lays new emphasis on the latter's relevance to contemporary social theory.