Macaulay was Secretary to the Board of Control under Lord Grey from 1832 until 1833. After the passing of the Government of India Act 1833, he was appointed as the first Law Member of the Governor - General's Council. He went to India in 1834. Serving on the Supreme Council of India between 1834 and 1838 he was instrumental in creating the foundations of bilingual colonial India, by convincing the Governor - General to adopt English as the medium of instruction in higher education, from the sixth year of schooling onwards, rather than Sanskrit or Persian then used in the institutions supported by the East India Company. By doing so, Macaulay wanted to "educate a people who cannot at present be educated by means of their mother tongue" and thus, by incorporating English, he sought to enrich the Indian languages so "that they could become vehicles for European scientific, historical, and literary expression". His final years in India were devoted to the creation of a Penal Code, as the leading member of the Law Commission.

In the aftermath of the Indian Mutiny of 1857, Macaulay's criminal law proposal was enacted. The Indian Penal Code (1860) was followed by the Criminal Procedure Code, 1872 and the Civil Procedure Code, 1909. The Indian Penal Code was later reproduced in most other British colonies – and to date many of these laws are still in effect in places as far apart as Pakistan, Singapore, Bangladesh, Sri Lanka, Nigeria and Zimbabwe as well as in India.

The term "Macaulay's Children" is used to refer to people born of Indian ancestry who adopt Western culture as a lifestyle, or display attitudes influenced by colonisers. It is used as a pejorative term, and the connotation is one of disloyalty to one's country and one's heritage. This frame of mind or attitude is also referred to as Macaulayism.

The passage to which the term refers is from his Minute on Indian Education, delivered in 1835. It reads,

Macaulay's Minute formed the basis for the reforms introduced in the English Education Act of 1835. In 1836, a school named La Martiniere which was founded by Major General Claude Martin had one of its houses named after him.

In independent India, Macaulay's idea of the civilizing mission has been used by Dalitists, in particular by neoliberalist Chandra Bhan Prasad, as a "creative appropriation for self - empowerment", based on the weltanschauung that Dalit folk are "empowered" by an English education as opposed to that in languages used traditionally (Sanskrit and Persian).

Returning to Britain in 1838, he became MP for Edinburgh. He was made Secretary at War in 1839 by Lord Melbourne and was sworn of the Privy Council the same year. In 1841 Macaulay addressed the issue of copyright law. Macaulay's position, slightly modified, became the basis of copyright law in the English speaking world for many decades. Macaulay argued that copyright is a monopoly and as such has generally negative effects on society. After the fall of Melbourne's government in 1841 Macaulay devoted more time to literary work, but returned to office as Paymaster - General in 1846 in Lord John Russell's administration.

In the election of 1847 he lost his seat in Edinburgh. He attributed the loss to the anger of religious zealots over his speech in favour of expanding the annual grant to Maynooth College in Ireland, which trained young men for the Catholic priesthood; some observers also attributed his loss to his neglect of local issues. In 1849 he was elected Rector of the University of Glasgow, a position with no administrative duties, often awarded by the students to men of political or literary fame; he also received the freedom of the city. In 1852, the voters of Edinburgh offered to re-elect him to Parliament. He accepted on the express condition that he need not campaign and would not pledge himself to a position on any political issue. Remarkably, he was elected on those terms. However, he seldom attended the House, due to ill health; indeed his weakness after suffering a heart attack caused him to postpone for several months making his speech of thanks to the Edinburgh voters. He resigned his seat in January, 1856. In 1857 he was raised to the peerage as Baron Macaulay, of Rothley in the County of Leicester, but seldom attended the House of Lords.

As a young man he composed the ballads Ivry and The Armada, which he later included as part of Lays of Ancient Rome, a series of very popular ballads about heroic episodes in Roman history which he composed in India and published in 1842. The most famous of them, Horatius, concerns the heroism of Horatius Cocles. It contains the oft-quoted lines:

Then out spake brave Horatius,
The Captain of the Gate:
"To every man upon this earth
Death cometh soon or late.
And how can man die better
Than facing fearful odds,
For the ashes of his fathers,
And the temples of his gods?"

During the 1840s he began work on his most famous work, The History of England from the Accession of James the Second, publishing the first two volumes in 1848. At first, he had planned to bring his history down to the reign of George III. After publication of his first two volumes, his hope was to complete his work with the death of Queen Anne in 1714. The third and fourth volumes, bringing the history to the Peace of Ryswick, were published in 1855. However, at his death in 1859, he was working on the fifth volume. This, bringing the History down to the death of William III, was prepared for publication by his sister, Lady Trevelyan, after his death.

Macaulay's political writings are famous for their ringing prose and for its confident, sometimes dogmatic, emphasis on a progressive model of British history, according to which the country threw off superstition, autocracy and confusion to create a balanced constitution and a forward looking culture combined with freedom of belief and expression. This model of human progress has been called the Whig interpretation of history. This philosophy appears most clearly in the essays Macaulay wrote for the Edinburgh Review. But it is also reflected in the History; the most stirring passages in the work are those that describe the "Glorious Revolution" of 1688. Macaulay's approach has been criticised by later historians for its one - sidedness and its complacency. Karl Marx referred to him as a 'systematic falsifier of history'. His tendency to see history as a drama led him to treat figures whose views he opposed as if they were villains, while characters he approved of were presented as heroes. Macaulay goes to considerable length, for example, to absolve his main hero William III of any responsibility for the Glencoe massacre. Winston Churchill devoted a four volume biography of the Duke of Marlborough to rebutting Macaulay's slights of his ancestor, expressing hope 'to fasten the label "Liar" to his genteel coat - tails.' On the other hand, this outlook, together with his obvious love of his subject matter and of English civilization, helps to place the reader within the age being described in a personal way that no cold neutrality could, and Macaulay's History is generally recognized as one of the masterpieces of historical writing and a magisterial literary triumph only comparable as such to Gibbon and Michelet.

Macaulay sat on the committee to decide on subjects from British history to be painted in the new Palace of Westminster. The need to collect reliable portraits of noted figures in British history for this project led to the foundation of the National Portrait Gallery, which was formally established on 2 December 1856. Macaulay was amongst its founder trustees and is honoured with one of only three busts above the main entrance.

During later years his health made work increasingly difficult for him. He died in December 1859, aged 59, leaving his major work, The History of England from the Accession of James the Second incomplete. He was buried in Westminster Abbey. As he had no children, his peerage became extinct on his death.

Macaulay's nephew, Sir George Trevelyan, Bt, wrote a best - selling "Life and Letters" of his famous uncle, which is still the best complete life of Macaulay. His great - nephew was the Cambridge historian G.M. Trevelyan.

The Liberal historian Lord Acton read Macaulay's History of England four times and later described himself as "a raw English schoolboy, primed to the brim with Whig politics" but "not Whiggism only, but Macaulay in particular that I was so full of". However after coming under German influence Acton would later find fault in Macaulay. In 1880 Acton classed Macaulay (with Burke and Gladstone) as one "of the three greatest Liberals". In 1883 he advised Mary Gladstone "that the Essays are really flashy and superficial. He was not above par in literary criticism; his Indian articles will not hold water; and his two most famous reviews, on Bacon and Ranke, show his incompetence. The essays are only pleasant reading, and a key to half the prejudices of our age. It is the History (with one or two speeches) that is wonderful. He knew nothing respectably before the seventeenth century, he knew nothing of foreign history, of religion, philosophy, science, or art. His account of debates has been thrown into the shade by Ranke, his account of diplomatic affairs, by Klopp. He is, I am persuaded, grossly, basely unfair. Read him therefore to find out how it comes that the most unsympathetic of critics can think him very nearly the greatest of English writers". In 1885 Acton asserted that: "We must never judge the quality of a teaching by the quality of the Teacher, or allow the spots to shut out the sun. It would be unjust, and it would deprive us of nearly all that is great and good in this world. Let me remind you of Macaulay. He remains to me one of the greatest of all writers and masters, although I think him utterly base, contemptible and odious for certain reasons which you know". In 1888 he wrote that Macaulay "had done more than any writer in the literature of the world for the propagation of the Liberal faith, and he was not only the greatest, but the most representative, Englishman then [1856] living".

Herbert Butterfield's The Whig Interpretation of History (1931) attacked Whig history. The Dutch historian Pieter Geyl, writing in 1955, considered Macaulay's Essays as "exclusively and intolerantly English".

George Richard Potter, Professor and Head of the Department of History at the University of Sheffield from 1931 to 1965, claimed "In an age of long letters... Macaulay's hold their own with the best". However Potter also claimed: "For all his linguistic abilities he seems never to have tried to enter into sympathetic mental contact with the classical world or with the Europe of his day. It was an insularity that was impregnable... If his outlook was insular, however, it was surely British rather than English". He said this about Macaulay's determination to inspect physically the places mentioned in his History: "Much of the success of the famous third chapter of the History which may be said to have introduced the study of social history, and even... local history, was due to the intense local knowledge acquired on the spot. As a result it is a superb, living picture of Great Britain in the latter half of the seventeenth century... No description of the relief of Londonderry in a major history of England existed before 1850; after his visit there and the narrative written round it no other account has been needed... Scotland came fully into its own and from then until now it has been a commonplace that English history is incomprehensible without Scotland". Potter noted that Macaulay has had many critics, some of whom put forward some salient points about the deficiency of Macaulay's History but added: "The severity and the minuteness of the criticism to which the History of England has been subjected is a measure of its permanent value. It is worth very ounce of powder and shot that is fired again it". Potter concluded that "in the long roll of English historical writing from Clarendon to Trevelyan only Gibbon has surpassed him in security of reputation and certainty of immortality".

In 1972 J.R. Western wrote that: "Despite its age and blemishes, Macaulay's History of England has still to be superseded by a full scale modern history of the period". In 1974 J.P. Kenyon stated that: "As is often the case, Macaulay had it exactly right".

W.A. Speck wrote in 1980 that Macaulay's History of England "still commands respect is that it was based upon a prodigious amount of research". Speck claims that "Macaulay's reputation as an historian has never fully recovered from the condemnation it implicitly received in Herbert Butterfield's devastating attack on The Whig Interpretation of History. Though he was never cited by name, there can be no doubt that Macaulay answers to the charges brought against Whig historians, particularly that they study the past with reference to the present, class people in the past as those who furthered progress and those who hindered it, and judge them accordingly". Speck also said that Macaulay too often "denies the past has its own validity, treating it as being merely a prelude to his own age. This is especially noticeable in the third chapter of his History of England, when again and again he contrasts the backwardness of 1685 with the advances achieved by 1848. Not only does this misuse the past, it also leads him to exaggerate the differences". Although Speck also wrote that Macaulay "took pains to present the virtues even of a rogue, and he painted the virtuous warts and all", and that "he was never guilty of suppressing or distorting evidence to make it support a proposition which he knew to be untrue". Speck concluded: "What is in fact striking is the extent to which his History of England at least has survived subsequent research. Although it is often dismissed as inaccurate, it is hard to pinpoint a passage where he is categorically in error... his account of events has stood up remarkably well... His interpretation of the Glorious Revolution also remains the essential starting point for any discussion of that episode... What has not survived, or has become subdued, is Macaulay's confident belief in progress. It was a dominant creed in the era of the Great Exhibition. But Auschwitz and Hiroshima destroyed this century's claim to moral superiority over its predecessors, while the exhaustion of natural resources raises serious doubts about the continuation even of material progress into the next."

In 1981 J. W. Burrow argued that Macaulay's History of England:

...is not simply partisan; a judgement, like that of Firth, that Macaulay was always the Whig politician could hardly be more inapposite. Of course Macaulay thought that the Whigs of the seventeenth century were correct in their fundamental ideas, but the hero of the History was William, who, as Macaulay says, was certainly no Whig... If this was Whiggism it was so only, by the mid - nineteenth century, in the most extended and inclusive sense, requiring only an acceptance of parliamentary government and a sense of gravity of precedent. Butterfield says, rightly, that in the nineteenth century the Whig view of history became the English view. The chief agent of that transformation was surely Macaulay, aided, of course, by the receding relevance of seventeenth - century conflicts to contemporary politics, as the power of the crown waned further, and the civil disabilities of Catholics and Dissenters were removed by legislation. The History is much more than the vindication of a party; it is an attempt to insinuate a view of politics, pragmatic, reverent, essentially Burkean, informed by a high, even tumid sense of the worth of public life, yet fully conscious of its interrelations with the wider progress of society; it embodies what Hallam had merely asserted, a sense of the privileged possession by Englishmen of their history, as well as of the epic dignity of government by discussion. If this was sectarian it was hardly, in any useful contemporary sense, polemically Whig; it is more like the sectarianism of English respectability.

In 1982 Gertrude Himmelfarb wrote that "most professional historians have long since given up reading Macaulay, as they have given up writing the kind of history he wrote and thinking about history as he did. Yet there was a time when anyone with any pretension to cultivation read Macaulay". Himmelfarb also laments that "the history of the History is a sad testimonial to the cultural regression of our times".