The only son of John Hallam, canon of Windsor and dean of Bristol, Henry Hallam was educated at Eton and Christ Church, Oxford, graduating in 1799. Called to the bar, he practised for some years on the Oxford circuit; but his tastes were literary, and when, on his father's death in 1812, he inherited a small estate in Lincolnshire, he gave himself up to study. He had become connected with the brilliant band of authors and politicians who led the Whig party, a connection to which he owed his appointment to the well-paid and easy post of commissioner of stamps; but took no part in politics himself. He was, however, an active supporter of many popular movements—particularly of that which ended in the abolition of the slave trade; and he was attached to the political principles of the Whigs.
Hallam's earliest literary work was undertaken in connection with the Whig periodical, the Edinburgh Review, where his review of Walter Scott's Dryden attracted attention. His first major work, The View of the State of Europe during the Middle Ages, was produced in 1818, and was followed nine years later by the Constitutional History of England. In 1838–1839 appeared the Introduction to the Literature of Europe in the 15th, 16th and 17th Centuries. A volume of supplemental notes to his Middle Ages was published in 1843; these facts and dates represent nearly all of Hallam's career.
Hallam lost his children, one after another. His eldest son, Arthur Henry Hallam--the "A.H.H." of Tennyson's In Memoriam—died in 1833 at the age of twenty-two. Seventeen years later, his second son, Henry Fitzmaurice Hallam, was cut off like his brother at the start of a career. He survived his wife (Julia Maria, daughter of Sir Charles Elton), daughter and sons by many years.
In 1834 Hallam published The Remains in Prose and Verse of Arthur Henry Hallam, with a Sketch of his Life. In 1852 a selection of Literary Essays and Characters from the Literature of Europe was published.
The Middle Ages is described by Hallam himself as a series of historical dissertations, for the period from the 5th to the 15th century. The work consists of nine long chapters: the histories of France, Italy, Spain, Germany, and of the Greek and Saracenic empires, fill five chapters. Others deal with major institutional features of medieval society: the feudal system, the ecclesiastical system, and the political system of England. The last chapter sketches society, commerce, manners, and literature in the Middle Ages.
The Constitutional History of England takes up the subject at the point at which it had been dropped in the View of the Middle Ages, namely the accession of Henry VII, and carries it down to the accession of George III. Hallam stopped here because he was unwilling to touch on issues of contemporary politics which seemed to him to run back through the whole period of the reign of George III; and he was accused of bias. The Quarterly Review for 1828 contains a hostile article on the Constitutional History, written by Southey, full of reproach: the work, he said, is the "production of a decided partisan." It was his distant treatment of Charles I, Cranmer and Laud that provoked the indignation of Southey.
Hallam, like Macaulay, ultimately referred political questions to the standard of Whig constitutionalism. But he was conscientious with his materials; and it was this which made the Constitutional History one of the standard text-books of English politics.
The Introduction to the Literature of Europe continues a topic broached in the View of the Middle Ages. In the first chapter Hallam sketches the state of literature in Europe down to the end of the 14th century: the extinction of ancient learning which followed the fall of the Roman empire and the rise of Christianity; the preservation of the Latin language in the services of the church; and the revival of letters after the 7th century. For the first century and a half of his period he is mainly occupied with a review of classical learning, taking short decennial periods and noticing works which they produced. For the period 1520–1550 there are separate chapters on ancient literature, theology, science, speculative philosophy and jurisprudence, the literature of taste and other miscellaneous literature; and the subdivisions of subjects is carried further in later periods. Thus poetry, the drama and polite literature form the subjects of separate chapters. An author may be mentioned in many chapters: Shakespeare, Grotius, Francis Bacon and Thomas Hobbes appear in half a dozen different places. 
The plan excluded biographical history. It is an account of the books which would make a complete library of the period, arranged according to date of publication and subject.
- Robertson 1911, p. 851.
- Robertson 1911, p. 851 notes that Lord Brougham, overlooking the constitutional chapter in the Middle Ages, censured Hallam for making an arbitrary beginning at the reign of Henry VII, and proposed to write a more complete history himself.
- Robertson 1911, pp. 851, 852.
- Robertson 1911, p. 852.
- Stephen, Leslie (1890). "Hallam, Henry". In Leslie Stephen and Sidney Lee. Dictionary of National Biography 24. London: Smith, Elder & Co. p. 96.
- This article incorporates text from a publication now in the public domain: Robertson, Edmund (1911). "Hallam, Henry". In Chisholm, Hugh. Encyclopædia Britannica 12 (11th ed.). Cambridge University Press. pp. 851, 852.
- Macaulay, Thomas Babbington (September 1828). "Hallam's 'Constitutional History'". Critical and Historical essays: English History 1. Retrieved November 2011.
- Landry, Peter (2011). "The Legal Philosophers, Or The Jurists: Hallam, Henry (1777-1859)". Blupete website. Retrieved November 2011.