The brilliant historian E. J. Hobsbawm (1917-2012; NYT obit here) joined the Communist Party (CP) as a student at Cambridge, having earlier been a member of a Communist student group as a teenager in Germany. The brilliant novelist and philosopher Iris Murdoch (1919-1999) joined the CP as a student at Oxford. Their paths crossed briefly: Murdoch's biographer Peter Conradi notes that after her first year at Oxford, in the summer of 1939, she "attended a one-week Communist Party summer school in Surrey, where the future historian Eric Hobsbawm, then studying at Cambridge, was deeply impressed by her looks, character and intelligence...." (Iris Murdoch: A Life, p.98, citing a 1999 interview with Hobsbawm)
Not too long thereafter their political trajectories diverged. Hobsbawm stayed in the Party for most of his life, whereas Murdoch left the CP before the Second World War ended. Hobsbawm's recent death brought out critics who charged him with blindness to the horrors of Stalinism, a charge that does not affect the bulk of his historical work, including the well-known three volumes on 'the long nineteenth century'. (To quote the NYT obit, "in 1994 [Hobsbawm] shocked viewers when, in an interview with Michael Ignatieff on the BBC, he said that the deaths of millions of Soviet citizens under Stalin would have been worth it if a genuine Communist society had been the result." On the other hand, in The Age of Extremes, p.380, Hobsbawm wrote of Stalin that "few men have manipulated terror on a more universal scale.")
As for Iris Murdoch's politics, they turned into fairly standard liberalism, in more or less the American sense of that word (see, e.g., the chapter on politics in her Metaphysics as a Guide to Morals), though she was much more interested in ethics and aesthetics than political theory. Peter Conradi writes: "It could be said that all [Murdoch's] fiction, and much of her moral philosophy, are acts of penance for, and attacks upon, the facile rationalistic optimism of her extreme youth...." (Iris Murdoch: A Life, p.78) That may be a bit of an overstatement but there is something in it, as anyone can attest who is familiar with, to take just one of many possible examples, Murdoch's portrait of the revolutionary theorist Crimond in The Book and the Brotherhood. Her novels do not, for the most part, take much notice of world events; an exception, The Accidental Man, in which the Vietnam War complicates the moral and practical life of a young American intellectual living in Britain, proves the rule.
Hobsbawm and Murdoch, markedly different in their interests and outlooks for most of their lives, wrote completely different kinds of books which are united only by the probability that people will still be reading them a hundred years from now. They are two of many gifted people for whom the Communist Party seemed, in the era of Depression and fascism, the right and necessary political choice.
P.s. on Hobsbawm: The first sentence of the NYT obituary (linked above) refers to his "three-volume economic history of the rise of industrial capitalism." This is not a wholly accurate description of the "Age of..." volumes. I was glancing at my old paperback copy of The Age of Revolution several days ago, and it appears that some of the most engaging writing in it is in the chapter on the arts (ch.14).