This paper revisits why Joan Robinson turned to Karl Marx in 1942 and which insights from Marxian economics she sought to incorporate into her later works, while commenting on the legacies of this encounter and how was received by some her of contemporaries. By the end of the 1930s, Robinson wanted to bring academic and Marxian economics together in a search for a more realist theory of the rate of profit and income distribution, and clarifications on Keynes’s concept of full employment, the nature of technical progress and a long-period theory within the Keynesian framework. The result, An Essay on Marxian Economics (1942), was her most important work in terms of laying the foundations of her enduring challenge to the orthodox economics. Here she relied on Marxian insights to escape Marshallian orthodoxy. It is the story of how the originator of imperfect competition pushed further into a theory of exploitation.