Initially a supporter of neoclassical economics, she changed her mind after getting acquainted with John Maynard Keynes. As a member of "the Cambridge School" of economics, Robinson assisted with the support and exposition of Keynes' General Theory, writing especially on its employment implications in 1936 and 1937 (it attempted to explain employment dynamics in the midst of the Great Depression).

In 1933, in her book, The Economics of Imperfect Competition, Robinson coined the term "monopsony," which is used to describe the buyer converse of a seller monopoly.

In 1942 Robinson's An Essay on Marxian Economics famously concentrated on Karl Marx as an economist, helping revive the debate on this aspect of his legacy.

During the Second World War, Joan Robinson worked on a few different Committees for the wartime national government. During this time, she visited the Soviet Union as well as China. She developed an interest in underdeveloped and developing nations and contributed a lot that is now understood in this section of economics.

In 1949, she was invited by Ragnar Frisch to become the vice president of the Econometric Society but declined, saying she couldn't be part of the editorial committee of a journal she couldn't read.

In 1956, Joan Robinson published her magnum opus, The Accumulation of Capital, which extended Keynesianism into the long-run. Six years later, she published another book about growth theory, which talked about concepts of "Golden Age" growth paths. Afterwards, she developed the Cambridge growth theory with Nicholas Kaldor. During the 1960s, she was a major participant in the Cambridge capital controversy alongside Piero Sraffa.

Close to the end of her life she studied and concentrated on methodological problems in economics and tried to recover the original message of Keynes' General Theory. Between 1962 and 1980 she wrote many economics books for the general public. Robinson suggested developing an alternative to the revival of classical economics.

At least two students who studied under her have won the Nobel Prize in Economic Sciences: Amartya Sen and Joseph Stiglitz.

Also, Robinson made several trips to China, reporting her observations and analyses in China: An Economic Perspective (1958), The Cultural Revolution in China (1969), and Economic Management in China (1975; 3rd ed, 1976), in which she praised the Cultural Revolution. She also stated in reference to divided Korea that "[o]bviously, sooner or later the country must be reunited by absorbing the South into socialism." These statements caused significant damage to her reputation, and possibly cost her the Nobel Prize for Economics. During her last decade, she became more and more pessimistic about the possibilities of reforming economic theory, as expressed, for example, in her essay "Spring Cleaning".