Thomas was a weak and sickly child. His youth was spent in solitude, and when his elder brother, William, came home, he wreaked havoc in the quiet surroundings. De Quincey's mother (who counted Hannah More amongst her friends) was a woman of strong character and intelligence, but seems to have inspired more awe than affection in her children. She brought them up very strictly, taking Thomas out of school after three years because she was afraid he would become big-headed, and sending him to an inferior school at Winkfield in Wiltshire.
In 1800, De Quincey, aged fifteen, was ready for the University of Oxford; his scholarship was far in advance of his years. "That boy," his master at King Edward's School had said, "could harangue an Athenian mob better than you or I could address an English one." He was sent to Manchester Grammar School, in order that after three years' stay he might obtain a scholarship to Brasenose College, Oxford, but he took flight after nineteen months.
His first plan had been to reach William Wordsworth, whose Lyrical Ballads (1798) had consoled him in fits of depression and had awakened in him a deep reverence for the poet. But for that De Quincey was too timid, so he made his way to Chester, where his mother dwelt, in the hope of seeing a sister; he was caught by the older members of the family, but, through the efforts of his uncle, Colonel Penson, received the promise of a guinea a week to carry out his later project of a solitary tramp through Wales. From July to November, 1802, De Quincey lived as a wayfarer. He soon lost his guinea by ceasing to keep his family informed of his whereabouts, and had difficulty making ends meet. Still apparently fearing pursuit, he borrowed some money and travelled to London, where he tried to borrow more. Having failed, he lived close to starvation rather than return to his family.
This period of privation left a profound mark upon De Quincey's psychology, and upon the writing he would later do; it forms a major and crucial part of the first section of the Confessions, and re-appears in various forms throughout the vast body of his lifetime literary work.
Discovered by chance by his friends, De Quincey was brought home and finally allowed to go to Worcester College, Oxford, on a reduced income. Here, we are told, "he came to be looked upon as a strange being who associated with no one." During this time he began to take opium. He completed his studies, but failed to take the oral examination leading to a degree; he left the university without graduating. He became an acquaintance of Samuel Taylor Coleridge and William Wordsworth, having already sought out Charles Lamb in London. His acquaintance with Wordsworth led to his settling in 1809 at Grasmere, in the beautiful English Lake District; his home for ten years was Dove Cottage, which Wordsworth had occupied and which is now a popular tourist attraction. De Quincey was married in 1816, and soon after, having no money left, he took up literary work in earnest.
(His wife Margaret bore him eight children before her death in 1837. Five, however, predeceased their father; three of De Quincey's daughters survived him.)
From this time on De Quincey maintained himself by contributing to various magazines. He soon exchanged London and the Lakes for Edinburgh and its suburb Lasswade, and Glasgow; he spent the remainder of his life in Scotland. Blackwood's Edinburgh Magazine and its rival Tait's Magazine received a large number of contributions. Suspiria de Profundis (1845) appeared in Blackwood's, as did The English Mail-Coach (1849). Joan of Arc (1847) was published in Tait's. Between 1835 and 1849, Tait's published a series of De Quincey's reminiscences of Wordsworth, Coleridge, Robert Southey, and other figures among the Lake Poets — a series that taken together constitutes one of his most important works.
De Quincey came into his patrimony at the age of 21, when he received ₤2000 from his late father's estate. He was unwisely generous with his funds, making loans that could not or would not be repaid, including a ₤300 loan to Coleridge in 1807. After leaving Oxford without a degree, he made an attempt to study law, but desultorily and unsuccessfully; he had no steady income and spent large sums on books (he was a lifelong collector). By the 1820s he was constantly in financial difficulties. More than once in his later years, De Quincey was forced to seek protection from arrest in the debtors' sanctuary of Holyrood in Edinburgh. (At the time, Holyrood Palace and Holyrood Park together formed a debtors' sanctuary; people could not be arrested for debt within those bounds. The debtors who took sanctuary there could only emerge on Sundays, when arrests for debt were not allowed.) Yet De Quincey's money problems persisted; he got into further difficulties for debts he acquired within the sanctuary.
His financial situation improved only later in his life. His mother's death in 1846 brought him an income of ₤200 per year. When his daughters matured, they managed his budget more responsibly than he ever had himself.
As with many addicts, De Quincey's opium addiction may have had a "self-medication" aspect for real physical illnesses, as well as a psychological aspect. Psychologically, he had what Alethea Hayter has called the "pariah temperament" typical of drug addicts.
By his own testimony, De Quincey first used opium in 1804 to relieve his neuralgia; he used it for pleasure, but no more than weekly, through 1812. It was in 1813 that he first commenced daily usage, in response to illness and his grief over the death of Wordsworth's young daughter Catherine. In the periods of 1813–16 and 1817–19 his daily dose was very high, and resulted in the sufferings recounted in the final sections of his Confessions. For the rest of his life his opium use fluctuated between extremes; he took "enormous doses" in 1843, but late in 1848 he went for 61 days with none at all. Notably, his periods of low usage were literarily unproductive.
The existence of the American edition provoked and prompted a corresponding British edition. Since the Spring of 1850 De Quincey had been a regular contributor to an Edinburgh periodical called Hogg's Weekly Instructor; publisher James Hogg undertook to publish a collected edition of De Quincey's work, under the cumbersome title Selections Grave and Gay from Writings Published and Unpublished by Thomas De Quincey. De Quincey edited and sometimes re-wrote his works for the Hogg edition; the 1856 second edition of the Confessions was prepared for inclusion in Selections Grave and Gay. The first volume of that edition appeared in May 1853, and the fourteenth and last in January 1860, a month after the author's death.
Both of these were multi-volume collections, but made no pretense to be "complete" editions. Scholar and editor David Masson attempted a more definitive collection: The Works of Thomas De Quincey appeared in fourteen volumes in 1889 and 1890. Yet De Quincey's writings were so voluminous and widely-dispersed that further collections followed: two volumes of The Uncollected Writings (1890), and two volumes of Posthumous Works (1891–93). De Quincey's 1803 diary was published in 1927. Yet another volume, New Essays by De Quincey, appeared in 1966.