From 1803 to 1806 he was editor of an ambitious periodical called the Literary Journal, which professed to give a summary view of all the leading departments of human knowledge. During this time he also edited the St James's Chronicle, belonging to the same proprietor. In 1804 he wrote a pamphlet on the corn trade, arguing against a bounty on the exportation of grain. In 1805 he published a translation (with notes and quotations) of CF Villers's work on the Reformation, an unsparing exposure of the alleged vices of the papal system.

In 1805 he married Harriet Burrow, whose mother, a widow, kept an establishment for lunatics in Hoxton. He then took a house in Pentonville, where his eldest son, John Stuart Mill, was born in 1806. About the end of this year he began his History of India, which he took twelve years to complete, instead of three or four, as had been expected.

In 1808 he became acquainted with Jeremy Bentham, and was for many years his chief companion and ally. He adopted Bentham's principles in their entirety, and determined to devote all his energies to bringing them before the world. Between 1806 and 1818 he wrote for the Anti-Jacobin Review, the British Review and the Electric Review; but there is no means of tracing his contributions.

In 1808 he began to write for the Edinburgh Review, to which he contributed steadily till 1813, his first known article being "Money and Exchange." He also wrote on Spanish America, China, General Miranda, the East India Company, and the Liberty of the Press. In the Annual Review for 1808 two articles of his are traced--a "Review of Fox's History," and an article on "Bentham's Law Reforms," probably his first published notice of Bentham. In 1811 he co-operated with William Allen (1770-1843), quaker and chemist, in a periodical called the Philanthropist.

He contributed largely to every number--his principal topics being Education, Freedom of the Press, and Prison Discipline (under which he expounded Bentham's Panopticon). He made powerful onslaughts on the Church in connexion with the Bell and Lancaster controversy, and took a prominent part in the discussions which led to the foundation of the University of London in 1825. In 1814 he wrote a number of articles, containing an exposition of utilitarianism, for the supplement to the fifth edition of the Encyclopædia Britannica, the most important being those on "Jurisprudence," "Prisons" and "Government."

In 1818 the History of India was published, and obtained a great and immediate success. It brought about a change in the author's position. The year following he was appointed an official in the India House, in the important department of the examiner of Indian correspondence. He gradually rose in rank till he was appointed, in 1830, head of the office, with a salary of £1900, raised in 1836 to £2000. His great work, the Elements of Political Economy, appeared in 1821 (3rd and revised ed. 1825).

From 1824 to 1826 Mill contributed to the Westminster Review, started as the organ of his party, a number of articles in which he attacked the Edinburgh and Quarterly Reviews and ecclesiastical establishments. In 1829 appeared the Analysis of the Phenomena of the Human Mind. From 1831 to 1833 Mill was largely occupied in the defence of the East India Company, during the controversy attending the renewal of its charter, he being in virtue of his office the spokesman of the court of directors. For the London Review, founded by Sir William Molesworth in 1834, he wrote a notable article entitled "The Church and its Reform," which was much too sceptical for the time, and injured the Review. His last published book was the Fragment on Mackintosh (1835).

Mill had a thorough acquaintance with Greek and Latin literature, general history, political, mental and moral philosophy. His intellect was logical in the highest degree; he was clear and precise, an enemy of loose reasoning, and quick to refute prevailing fallacies. All his work is marked by original constructive thought, except in a few subjects, in which he confessedly expounded Bentham's views.

At a time when social subjects were as a rule treated empirically, he brought first principles to bear at every point. His greatest literary monument is the History of India. The materials for narrating the acquisition by the United Kingdom of its Indian Empire were put into shape for the first time; a vast body of political theory was brought to bear on the delineation of the Hindu civilization; and the conduct of the actors in the successive stages of the conquest and administration of India was subjected to a severe criticism.

The work itself, and the author's official connexion with India for the last seventeen years of his life, effected a complete change in the whole system of governing that country. It is noteworthy that Mill never visited the Indian colony, relying solely on documentary material and archival records in compiling his work.

Mill played a great part also in British politics, and was, more than any other man, the founder of what was called "philosophic radicalism." His writings on government and his personal influence among the Liberal politicians of his time determined the change of view from the French Revolution theories of the rights of man and the absolute equality of men to the claiming of securities for good government through a wide extension of the franchise.

Under this banner it was that, the Reform Bill was fought and won. His Elements of Political Economy, which was intended only as a textbook of the subject, shows all the author's precision and lucidity. As Dr J. K. Ingram said, it has the "character of a work of art." It followed up the views of Ricardo, with whom Mill was always on terms of intimacy. Its interest is mainly historical, as an accurate summary of views which are now largely discarded. Among the more important of its theses are:

1. that the chief problem of practical reformers is to limit the increase of population, on the assumption that capital does not naturally increase at the same rate as population (ii. § 2, art. 3)
2. that the value of a thing depends entirely on the quantity of labour put into it; and
3. that what is now known as the "unearned increment" of land is a proper object for taxation.
4. The work as a whole is a striking example of the weakness of treating monomic problems from a purely a priori standpoint by the deductive method.

By his Analysis of the Mind and his Fragment on Mackintosh Mill acquired a position in the history of psychology and ethics. He took up the problems of mind very much after the fashion of the Scottish Enlightenment, as then represented by Thomas Reid, Dugald Stewart and Thomas Brown, but made a new start, due in part to David Hartley, and still more to his own independent thinking. He carried out the principle of association into the analysis of the complex emotional states, as the affections, the aesthetic emotions and the moral sentiment, all which he endeavoured to resolve into pleasurable and painful sensations.

But the salient merit of the Analysis is the constant endeavour after precise definition of terms and clear statement of doctrines. The Fragment on Mackintosh is a severe exposure of the flimsiness and misrepresentations of Sir James Mackintosh's famous Dissertation on the Progress of Ethical Philosophy (1830), and discusses the foundations of ethics from the author's utilitarian point of view.