Chalmers was born at Fochabers, Moray, in 1742. His father, James Chalmers, was a grandson of George Chalmers of Pittensear, a small estate in the parish of Lhanbryde, now St Andrews-Lhanbryde, in Moray, owned by the family since the beginning of the 17th century. After completing the usual course at King's College, Aberdeen, the young Chalmers studied law at the University of Edinburgh for several years.
Two uncles on the father's side having settled in North America, he visited Maryland in 1763, apparently to assist in recovering a tract of land about which a dispute had arisen, and thus began practising as a lawyer at Baltimore, where for a time he met with much success. Having, however, espoused the cause of the Royalist party on the breaking out of the American War of Independence, he abandoned his professional prospects and returned to Great Britain. Several years elapsed before he obtained an appointment that placed him in a state of comfort and independence.
At length, in August 1786, Chalmers, whose sufferings as a Royalist must have strongly recommended him to the government of the day, was appointed chief clerk to the committee of Privy Council on matters relating to trade, a situation which he retained till his death in 1825, a period of nearly forty years. As his official duties made no great demands on his time, he had abundant leisure to devote to his favourite studies ... the antiquities and topography of Scotland having thenceforth special attractions for his busy pen.
On his death, his valuable and extensive library he bequeathed to his nephew, at whose death in 1841 it was sold and dispersed. Chalmers was a member of the Royal and Antiquarian Societies of London, an honorary member of the Antiquarian Society of Scotland, and a member of other learned societies. In private life he was undoubtedly an amiable man, although the dogmatic tone that disfigures portions of his writings procured him many opponents. Among his avowed antagonists in literary warfare the most distinguished were Edmond Malone and George Steevens, the Shakespeare edition; Mathias, the author of the Pursuits of Literature; Dr John Jamieson, the Scottish lexicographer; Pinkerton, the historian; Dr Irving, the biographer of the Scottish poets; and Dr Currie of Liverpool. But with all his failings in judgment Chalmers was a valuable writer. He uniformly had recourse to original sources of information; and he is entitled to great praise for his patriotic and self-sacrificing endeavours to illustrate the history, literature and antiquities of his native country.
Before his Privy Council appointment, Chalmers applied himself to investigating the history and establishment of the English colonies in North America. Enjoying free access to the state papers and other documents preserved among what were then termed the plantation records, he became possessed of much important information. His work, Political Annals of the present United Colonies from their Settlement to the Peace of 1763, (1780), was to have formed two volumes; but the second, which should have contained the period between 1688 and 1763, never appeared. The first volume, however, is complete in itself, and traces the original settlement of the different American colonies, and the progressive changes in their constitutions and forms of government as affected by the state of public affairs in the parent kingdom. Independently of its value as being compiled from original documents, it bears evidence of great research, and has been of essential benefit to later writers. Continuing his researches, he next gave to the world An Estimate of the Comparative Strength of Britain during the Present and Four Preceding Reigns (1782) which passed through several editions.
Besides biographical sketches of Defoe, Sir John Davies, Allan Ramsay, Sir David Lyndsay, Churchyard and others, prefixed to editions of their respective works, the British government paid Chalmers 500 pounds sterling to write a hostile biography of Thomas Paine, the author of the Rights of Man, that Chalmers published under the assumed name of Francis Oldys, A.M., of the University of Pennsylvania; and a life of Ruddiman, in which considerable light is thrown on the state of literature in Scotland during the earlier part of the last century. His life of Mary, Queen of Scots, was first published in 1818. It is founded on a manuscript left by John Whitaker, the historian of Manchester; but Chalmers found it necessary to rewrite the whole. Mary's history occupied much of his attention, and his last work, A Detection of the Love Letters lately attributed in Hugh Campbell's work to Mary Queen of Scots, is an exposure of an attempt to represent as genuine some fictitious letters said to have passed between Mary and Bothwell.
His Apology for the Believers in the Shakespeare Papers which were exhibited in Norfolk Street, appeared in 1797, followed by other tracts on the same subject. These contributions to the literature of Shakespeare seek to show that papers which had been proved forgeries might nevertheless have been genuine. Chalmers also took part in the controversy on the identity of Junius , and in The Author of Junius Ascertained, from a Concatenation of Circumstances amounting to Moral Demonstration (1817) sought to fix the authorship of the Junius letters on Hugh Boyd. In 1824 he published The Poetical Remains of some of the Scottish Kings, now first collected; and in the same year he edited and presented as a contribution to the Bannatyne Club Robene and Makyne and the Testament of Cresseid, by Robert Henryson.
His political writings are equally numerous. Among them may be mentioned Collection of Treaties between Great Britain and other Powers (1790); Vindication of the Privileges of the People in respect to the Constitutional Right of Free Discussion, etc. (1796), published anonymously; A Chronological Account of Commerce and Coinage in Great Britain from the Restoration till 1850 (1810); Opinions of Eminent Lawyers on various points of English Jurisprudence, chiefly concerning the Colonies, Fisheries, and Commerce of Great Britain (1814); Comparative Views of the State of Great Britain before and since the War (1817).
He had also been engaged on a history of Scottish poetry and a history of printing in Scotland. Each of them he thought likely to extend to two large quarto volumes, and on both he expended an unusual amount of enthusiasm and energy. He had also prepared for the press an elaborate history of the life and reign of David I. In his later researches he was assisted by his nephew James, son of Alexander Chalmers, writer in Elgin.
Chalmers's greatest work is his Caledonia; which, however, he did not live to complete. The first volume appeared in 1807, and is introductory to the others. It is divided into four books, treating successively of the Roman, the Pictish, the Scottish and the Scoto-Saxon periods, from 80 to 1306 AD. In these we are presented, in a condensed form, with an account of the people, the language and the civil and ecclesiastical history, as well as the agricultural and commercial state of Scotland during the first thirteen centuries of our era. Unfortunately the chapters on the Roman period are entirely marred by the author's having accepted as genuine Bertram's forgery Dc Situ Britanniae; but otherwise his opinions on controversial topics are worthy of much respect, being founded on a laborious investigation of all the original authorities that were accessible to him.
The second volume, published in 1810, gives an account of the seven southeastern counties of Scotland ... Roxburgh, Berwick, East Lothian , Edinburgh/Midlothian (all as "Edinburgh"), West Lothian , Peebles and Selkirk ... each of them being treated of as regards name, situation and extent, natural objects, antiquities, establishment as shires, civil history, agriculture, manufactures and trade, and ecclesiastical history.
In 1824, after an interval of fourteen years, the third volume appeared, giving, under the same headings, a description of the seven south-western counties ... Dumfries, Kirkcudbright, Wigtown, Ayr, Lanark, Renfrew and Dumbarton. In the preface to this volume the author states that the materials for the history of the central and northern counties were collected, and that he expected the work would be completed in two years, but this expectation was not realized.