Blake was born in London in 1757, and had an unconventional start in life. The son of a hosier, he was educated at home, and encouraged by his parents from an early age to collect prints of the works of Italian masters. Demonstrating an early talent for drawing, his father had him apprenticed to an engraver, an experience that William was to carry into his practice of illustrating all his own poetical works in later life.

As a result of an association with the radical publisher Joseph Johnson, Blake met many of the leading dissidents and freethinkers of the day. His thinking took on an anti-rational and anti-materialist tone, as he rejected the values of the industrial revolution, poured scorn on the findings of Newton's physics, and subscribed to a mystical version of Christianity propounded by the Swedish visionary Emanuel Swedenborg. A friendship with writer and early feminist Mary Wollstonecraft led Blake to espouse the rights of women and advocate an early form of free love, rejecting the demand of traditional morality for chastity outside the marriage bed.

In 1800, Blake moved into a cottage in the village of Felpham in Sussex owned by a minor poet, William Hayley, having accepted a commission to produce a series of portraits of poets for Hayley's library. It was while staying at Felpham that he wrote Milton.

In later life, Blake faded into tragic obscurity, his artistic works failing to sell and his poetry ignored by all but a small coterie of followers. Many considered his views and lifestyle to be so unorthodox as to make him virtually mad, and when he died in 1827, he was buried in an unmarked grave at Bunhill Fields in the City of London. Speaking the epitaph that has rung down the years, his contemporary William Wordsworth said of Blake: "There was no doubt that this poor man was mad, but there is something in the madness of this man which interests me more than the sanity of Lord Byron and Walter Scott."