Studying in Cambridge never meant just going to lectures, seminars and supervisions but participating in a host of events, ranging from concerts to debates. Keynes was admitted to the secretive Apostles, a club that was under the sway of the philosopher G.E. Moore. He had close ties with the cultural and literary world and later became a member of the Bloomsbury group, who had soaked up from Moore the belief that "one's prime objects in life were love, the creation and enjoyment of aesthetic experience and the pursuit of knowledge". Bloomsbury reacted against the conservative habits, traditions and conventions of the Victorian era and claimed nothing less than cultural superiority. In a 1938 essay looking back at his life, entitled "My early beliefs", Keynes bluntly calls this attitude "immoralism" and recognises that its total rejection of traditional morality probably went too far; it wasn't even faithful to Moore's example. But Keynes was still frivolous enough to admit that it was now too late to change him.

At the end of his studies in 1904, he went on taking classes in Cambridge, especially in philosophy. He also tried out economics but didn't like it. In the end, he decided to leave academia and applied for a government job. He was appointed to the India Office in 1906. However, he quickly grew so bored in the civil service that he began work on a PhD thesis on probability. This is the context in which he became aware of the difference between risk and uncertainty, between unknown future events that can be given numbered probabilities and those that cannot. Keynes used his dissertation to apply, unsuccessfully, for a fellowship at King's. In the end, Alfred Marshall offered him a post as a lecturer in economics, funded out of his and John Neville Keynes's own pockets. Luckily for Keynes, in those days economics wasn't yet fully established at Cambridge, otherwise this act of nepotism wouldn't have been possible. It was also hazardous: at this stage Keynes knew very little about economics. 

In 1909, Keynes's doctoral thesis on probability was finally accepted, but he had to make some corrections; it took him until 1921 to complete them. In 1911, he was nevertheless elected to a fellowship at King's; he remained a fellow for the rest of his life. 

But this way of life didn't last. In 1915 he was called back into government, to the Treasury. Among his responsibilities were the design of terms of credit between Britain and its First World War continental allies, and the acquisition of scarce currencies. 

What is more important, however, is the fact that after the war, Keynes was appointed financial representative to the 1919 Paris Peace Conference. With his unorthodox — and initially unpopular — views, which he set down in his book The Economic Consequences of the Peace later that year, he made enemies and gained notoriety. Keynes warned that crushing Germany financially was a bad idea, both for economic and political reasons. He found it inconsistent to demand high reparations and deprive the country of the means to earn the money necessary to be able to pay them, and he feared the germination of a desire for revenge. He was right, even if the rise of Hitler cannot be explained by the Treaty of Versailles alone.