Hazlitt came of Irish Protestant stock, and of a branch of it which moved in the reign of George I from the county of Antrim to Tipperary. His father went to the University of Glasgow (where he was contemporary with Adam Smith), graduated in about 1761, became a Unitarian, joined their ministry, and crossed over to England; being successively pastor at Wisbech in Cambridgeshire, at Marshfield in Gloucestershire, and at Maidstone. At Wisbech he married Grace Loftus, daughter of a farmer. Of their many children, only three survived infancy.
William, the youngest of these, was born in Mitre Lane, Maidstone. From Maidstone the family moved in 1780 to Bandon, Co. Cork; and from Bandon in 1783 to America, where Mr. Hazlitt preached, lectured, and founded the First Unitarian Church at Boston. In 1786-1787 the family returned to England and took up their abode at Wem, in Shropshire. The elder son, John, was now old enough to choose a vocation, and became a miniature-painter. The second child, Peggy, had begun to paint also, amateurishly in oils. William, aged eight--a child out of whose recollection all memories of Bandon and of America (save the taste of barberries) soon faded-- took his education at home and at a local school. His father intended him for the Unitarian ministry, and sent him to a seminary in London, Hackney College. He stayed there for only a year, but shortly after returning home, he decided to become a writer.
In 1796 Hazlitt was introduced to Samuel Taylor Coleridge and William Wordsworth. He was also interested in art, and visited his brother John, who was now apprenticed to Sir Joshua Reynolds. He became friendly with Charles and Mary Lamb, and in 1808 he married Sarah Stoddart, who was a friend of Mary's. They lived at Salisbury, but after three years he left her and began a journalistic career, writing for the Morning Chronicle, Edinburgh Review, The Times, etc. He published several volumes of essays, including The Round Table and Characters of Shakespeare's Plays, both in 1817. His best-known work is The Spirit of the Age (1825), a collection of contemporary portraits, including Lamb, Coleridge, Wordsworth, Jeremy Bentham, Sir Walter Scott, and others.