As globalization, union busting, and automation remake the world of work, leaving current and future generations to subsist on contingent and informal employment, can we still defend the idea of the working class as the principal agent of radical change? Does a “historic force,” as Eric Hobsbawm put it in 1995, still exist to support the socialist project? With few exceptions, Marxists have come late in the day to this existential debate, often armed with little more than philosophical slogans. This paper argues that, to confront the issue, we first need to specify a baseline of comparison: that is to say, a sophisticated understanding of how proletarian agency was construed in the era of classical socialism. Starting from scattered clues left by Marx and his successors, above all Rosa Luxemburg, this essay outlines a theory of class formation and socialist hegemony in consonance with the historical, revolutionary experience of the working class’s actual lives and ideas. The basic thesis is that “agency” in the last instance is conditioned by the development of the productive forces but activated by the convergence (or “overdeterminations”) of political, economic, and cultural struggles. Even in socialism’s classical era, workers’ power did not reside exclusively at the point of production in the great factories; urban movements and international solidarity campaigns were also crucibles of class consciousness, perhaps with the most immediate relevance to our brave new jobless world.