From 1921 to 1922 he studied in London at the London School of Economics. In 1922 he was appointed as Director of the provincial labour department in Milan, then as Professor in Political economy first in Perugia, and later in Cagliari, Sardinia. In Turin he had met Antonio Gramsci (the most important leader of Italian Communist Party). They became close friends, partly due to their shared ideological views—Sraffa was at this time a radical Marxist. He also was already in contact with Filippo Turati, perhaps the most important leader of Italian Socialist Party, whom he allegedly met and frequently visited in Rapallo, where his family had a holiday villa.
In 1925 he wrote about returns to scale and perfect competition, underlining some doubtful points of Alfred Marshall's theory of the firm. This work was completed in an article he published the following year.
In 1927, his as yet undiscussed theory of value, but also his risky political ideas and his compromising friendship with Gramsci (who had already been imprisoned by the fascists —notably, Sraffa had brought him the materials, literally pens and paper, with which Gramsci would write his Prison Notebooks), brought John Maynard Keynes to prudentially invite Sraffa to the University of Cambridge, where he was initially assigned a lectureship. After a few years, Keynes created ex novo for him the charge of Marshall Librarian. Sraffa joined the so-called "cafeteria group", together with Frank P. Ramsey and Ludwig Wittgenstein, a sort of informal club that discussed Keynes's theory of probability and Friedrich Hayek's theory on business cycles.
John Eatwell wrote of Sraffa's work on Ricardo
Economists disagree on whether Sraffa's work refutes neoclassical economics. Many post-Keynesian economists use Sraffa's critique as justification for abandoning neoclassical analysis and exploring other models of economic behavior. Others see his work as compatible with neoclassical economics, as developed in modern general equilibrium models. Nonetheless, Sraffa's work, particularly his interpretation of Ricardo and his Production of Commodities by Means of Commodities, is seen as the starting point of the Neo-Ricardian school in the 1960s.
Norman Malcolm famously credits Sraffa with providing Ludwig Wittgenstein with the conceptual break that founded the Philosophical Investigations, by means of a rude gesture on Sraffa's part:
Wittgenstein was insisting that a proposition and that which it describes must have the same 'logical form', the same 'logical multiplicity', Sraffa made a gesture, familiar to Neapolitans as meaning something like disgust or contempt, of brushing the underneath of his chin with an outward sweep of the finger-tips of one hand. And he asked: 'What is the logical form of that?'
Sraffa was described as a very intelligent man, with a proverbial shyness and a real devotion for study and books. His famous library contained more than 8,000 volumes, now partly in the Trinity College Library. A popular anecdote claims that Sraffa made successful long-term investments in Japanese government bonds that he bought the day after the nuclear bombing on Hiroshima and Nagasaki.
In 1972 he was awarded an honorary doctorate by Paris's university (Sorbonne), and in 1976 he received another one from Madrid's Complutense university.