In September 1867, when Dostoevsky began work on what was to become The Idiot, he was living in Switzerland with his new wife Anna Grigoryevna, having left Russia in order to escape his creditors. They were living in extreme poverty, and constantly had to borrow money or pawn their possessions. They were evicted from their lodgings five times for non-payment of rent, and by the time the novel was finished in January 1869 they had moved between four different cities in Switzerland and Italy. During this time Dostoevsky periodically fell into the grip of his gambling addiction and lost what little money they had on the roulette tables. He was subject to regular and severe epileptic seizures, including one while Anna was going into labor with their daughter Sofia, delaying their ability to go for a midwife. The baby died aged only three months, and Dostoevsky blamed himself for the loss.

Dostoevsky's notebooks of 1867 reveal deep uncertainty as to the direction he was taking with the novel. Detailed plot outlines and character sketches were made, but were quickly abandoned and replaced with new ones. In one early draft, the character who was to become Prince Myshkin is an evil man who commits a series of terrible crimes, including the rape of his adopted sister (Nastasya Filippovna), and who only arrives at goodness by way of his conversion through Christ. By the end of the year, however, a new premise had been firmly adopted. In a letter to Apollon Maykov, Dostoevsky explained that his own desperate circumstances had "forced" him to seize on an idea that he had considered for some time but had been afraid of, feeling himself to be artistically unready for it. This was the idea to "depict a completely beautiful human being". Rather than bring a man to goodness, he wanted to start with a man who was already a truly Christian soul, someone who is essentially innocent and deeply compassionate, and test him against the psychological, social and political complexities of the modern Russian world. It was not only a matter of how the good man responded to that world, but of how it responded to him. Devising a series of scandalous scenes, he would "examine each character's emotions and record what each would do in response to Myshkin and to the other characters." The difficulty with this approach was that he himself did not know in advance how the characters were going to respond, and thus he was unable to pre-plan the plot or structure of the novel. Nonetheless, in January 1868 the first chapters of The Idiot were sent off to The Russian Messenger.