At the early age of twenty-two Mr. Jamieson thus entered upon the sacred office of a minister. It was at that time one of peculiar difficulty among the Secession body; for the ferment produced in this country by the French Revolution, and the political suspicions which it diffused through the whole community, caused all who did not belong to the Established Church to be considered as disloyal, or at least discontented subjects. Mr. Jamieson, of course, was regarded, at his entrance into Forfar, as one who might become a teacher of sedition, as well as a preacher of the gospel of peace. But he had not been long there when his conduct disarmed the suspicious, and procured him general confidence and esteem; while his able clerical labours were rewarded with a full congregation and permanent usefulness. He thus made trial of his ministry for sixteen years, during which period he married the daughter of a neighbouring proprietor, who gladdened the course of his lone life, and died only a year before his own decease. It was in Forfar also that he commenced his life of authorship, and his first production was of a kind the least to be expected from a plodding, word-sifting antiquary—it was a poem! It was published in 1789, and entitled, the "Sorrows of Slavery, a Poem, containing a Faithful Statement of Facts respecting the Slave-trade." We suspect that, though most of our readers may have read the splendid lyrics of Cowper and Montgomery on the same subject, they have not chanced to light upon this production of Jamieson. He made another attempt of the same nature in 1798, when he published "Eternity, a Poem, addressed to Freethinkers and Philosophical Christians." But during the interval between these two attempts, his pen had been employed in more hopeful efforts. These were, in "Alarm to Britain; or, an Inquiry into the Causes of the Rapid Progress of Infidelity," which he published in 1795, and a "Vindication of the Doctrine of Scripture, and of the Primitive Faith concerning the Divinity of Christ, in reply to Dr. Priestley’s "History of Early Opinions," which appeared in the same year. The last was a work of great scholarship and research, as well as cogent argument; and in these departments, at least, he showed himself a full match for his formidable antagonist. Another work, which he published during his ministry in Forfar, was of a different bearing, as may be learned from its title, which was, "Sermons on the Heart."

By these labours Jamieson won for himself an honourable name in literature, that was especially grateful to the religious community to which he belonged, and they testified their feeling in a way that was not only creditable to him, but to themselves A call was sent to him in 1796, from the congregation in Nicolson Street, Edinburgh, whose pastor, the Rev. Mr. Banks, had left them for America. The Synod at the time judged his transfer from Forfar to Edinburgh inexpedient, and decided accordingly; but the Nicolson Street congregation thought otherwise, and renewed their call, and were successful, so that he was inducted as their minister in June, 1797. Jamieson’s clerical duties were thus multiplied by a new and more extensive field of labour; but he did not remit those literary exertions which had thus far been crowned with success. In 1799 he published his "Remarks on Rowland Hill’s Journal." In 1802 appeared his work, in two volumes octavo, entitled the "Use of Sacred History;" and in 1806, the "Important Trial in the Court of Conscience." His next work, and by far his most important, was the Etymological Dictionary of the Scottish Language." The Herculean attempt which he proposed to himself in this work, and which he has so successfully accomplished, was the following:—

1. To illustrate the words in their different significations, by examples from ancient and modern writers.

2. To show their affinity to those of other languages, and especially the northern.

3. To explain many terms which, though now obsolete in England, were formerly common to both countries.

4. To elucidate national rites, customs, and institutions, in their analogy to those of other nations.

The history of this national production of Jamieson is worthy of particular notice. When he first engaged in a task to which his early studies and pursuits had been so congenial, he had meant to produce nothing more than a work of small dimensions—a mere vocabulary or glossary of the Scottish tongue; and in the notes which he had prepared for the occasion, the names of his authorities were merely mentioned, without further reference. It was then suggested to him that the Dictionary would be more acceptable to the public, as well as more satisfactory as a standard, if he quoted those passages at full by which his definitions were confirmed. He acted upon this advice, being fully persuaded of its correctness, and the consequence was, that his drudgery was again to be undergone, and that, too, with many heavy additions, so that he went over the whole ground not only a second, but, in many cases, a third time. It was not wonderful if, under such a process, the result was two goodly quarto volumes, instead of a slim duodecimo. The new light, also, which broke upon him in the course of his studies, was sufficient to inspire him with tenfold ardour in the task. At the outset he had supposed, in common with the prevalent opinion, that the Scottish language was, in fact, no language at all, but a mere dialect of the Anglo-Saxon; and that, as such, its fountain was at no greater distance than England, and of no higher antiquity than the days of Hengist and Horsa. His interviews, however, with a learned Icelander, suggested another and more important theory: this was, that the primitive words of the Scottish dialect were not Saxon, nor even Celtic, but Gothic. Were the Lowlanders of Scotland, then, the descendants not merely of Anglo-Saxon captives and refugees, but of a still more illustrious race—even of those who conquered Rome herself; and opened the way to the regeneration of Europe? Such, he concluded, must be the case; and the only difficulty that remained was to prove it. This he endeavoured to accomplish, by demonstrating that the Picts were not a Celtic but a Gothic race; and that from them, and not the Welsh or the Saxon, we derive these peculiarities of the Scottish tongue. This theory, which he supported with a great amount of learning and probability, is published in his "Dissertation on the Origin of the Scottish Language," prefixed to the Dictionary. The Dictionary itself was published in 1808-1809, to which a Supplement, in two other quarto volumes, was added in 1825. As the first portion of the work was soon out of print, he published an abridgment of it in 1818, in one volume octavo. All this was an immense amount of labour for a single mind, and the literary world was astonished at his long-continued, unshrinking perseverance, as well as the successful termination that requited it. But still he never considered it completed, and continued his additions and improvements to the last; so that, at his death, two large volumes in manuscript had accumulated, nearly ready for the press. And besides all this, his antiquarian industry was employed upon other tasks of a kindred nature. In 1811 he published "An Historical account of the Ancient Culdees of Iona, and of their settlement in England, Scotland, and Ireland." In 1814 appeared his "Hermes Scythicus, or the Radical Affinities of the Greek and Latin languages to the Gothic." In 1817 he contributed to the Edinburgh Philosophical Transactions a paper "On the origin of Cremation, or Burning of the Dead." In the year following he unexpectedly appeared in a "Grammar of Rhetoric and Polite Literature." He also edited two important national productions which, on account of their obsolete language, were fast hastening into general forgetfulness. These were, the "Wallace" of Blind Harry, and the "Bruce" of Barbour.