Having completed the usual course of academical discipline at Glasgow, Mr Macknight went to Leyden, in order to prosecute the study of theology, to which he had shown an early attachment. While he remained in Holland, he had an opportunity of procuring many valuable books, written by foreign divines, which afterwards assisted his own labours in explaining Scripture. After his return to Scotland, having received from the presbytery of Irvine a license to preach the gospel, he was chosen to officiate at the Gorbals, a district of Glasgow; a situation which at that time could be held by a licentiate of the church, before being ordained to the pastoral function. On this occasion, one of the candidates was Mr Robert Henry, afterwards the well known historian of Great Britain. It chanced that the gentlemen who were thus placed in competition with each other at the commencement of life, were at last, after an interval of many years, associated as colleagues in the charge of the Old Church parish of Edinburgh.

From the Gorbals, Mr Macknight went to Kilwinning, in consequence of an invitation from Mr Fergusson, then minister of that place; and acted for some time as his assistant in the charge of the parish. Here he conducted himself with such propriety, that his character began to be established; and on the death of Mr Fisher, at Maybole, he obtained the vacant living there, with the concurring wish of the heritors and people. Of this charge, accordingly, he was ordained as minister, on the 10th of May, 1753. At Maybole, Mr Macknight continued sixteen years; and discharged the duties of the pastoral office with such assiduity and kindness, that, when he left it, he carried with him the affections and regret of all his flock, it may be mentioned, as a pleasing evidence of attachment, that when he proposed accepting a presentation to the living of Jedburgh, many respectable inhabitants of the parish of Maybole, joined together in earnestly soliciting him to remain as their pastor; and in order to obtain his compliance with this request, they offered, not only to augment the value of his income, but to provide him an assistant, should the state of his health render it necessary. This generous proposal, however, he judged it proper from prudential considerations, to decline.

It was at Maybole, that, amidst his professional occupations in a populous charge, Dr Macknight composed the first and second of his works. Of the former, indeed, or the Harmony of the Gospels, it appears from his papers, that the plan had been conceived by him so early as the third or fourth year of his attendance at the university; and from that time he began to collect materials for the publication. The first edition of this book was published in 1756. Although the plan of it differed considerably from that of former Harmonies, in supposing that the Evangelists have not neglected the order of time in the narration of events, the reception it met with from most competent judges was so favourable, that the author was encouraged to undertake a second edition, with considerable improvements and additions. This edition appeared in 1763. In the same year, was also published by Dr Macknight, another performance of great merit, entitled the Truth of the Gospel History, which had been the fruit of the author’s studies during the interval between the first and second editions of his Harmony. Its object is, to illustrate and confirm, both by argument and by appeal to the testimony of ancient authors, what are commonly arranged under the three great titles of the Internal, the Collateral, and the Direct Evidences of the Gospel History.

By these publications, Dr Macknight soon obtained a high reputation for theological learning. The university of Edinburgh conferred on him (among the first who obtained that distinction in Scotland) the degree of Doctor of Divinity; and he was, in 1769, chosen moderator of the General Assembly of the church of Scotland. During the course of the same year, he was translated to the parochial charge of Jedburgh; in which he remained about three years, and where he received from his people the most flattering tokens of respect and kindness. In 1772, he was elected one of the ministers of Edinburgh; a preferment for which he was chiefly indebted to the long-continued and steady friendship of the very respectable and highly esteemed family of Kilkerran. His first charge in Edinburgh was the parish of Lady Yester’s; from which he was translated, in 1778, to the Old Church, where he continued during the remainder of his life.

Besides performing the ordinary duties of the pastoral function, a minister of Edinburgh, in virtue of his office, is much occupied with public meetings on business of various kinds, especially the management of the different charitable foundations, which have long been the boast of the capital of Scotland. On these, accordingly, Dr Macknight, though he entertained some doubts respecting the good effects of such institutions, bestowed much of his attention; and his judicious counsels of management, were undoubtedly productive, at that time, of considerable benefit, in maintaining the strictness of their discipline, as well as the purity of their administration. Among other objects of such official care, is the fund established by act of parliament for a provision to the widows and children of ministers in the church of Scotland. As one of the trustees appointed by the act, he had long taken a leading part in conducting the business of this Charity; and after the death of Dr Webster, he was appointed joint collector with Sir H. Moncrieff Wellwood, Bart.

In the church courts he acted steadily on that system of ecclesiastical policy, which for many years had guided the decisions of the General Assembly. At the same time, he firmly resisted whatever appeared to him as any infringement on the constitutional law or practice of the church; and, accordingly, when some of his moderate friends wished for the abolition of Calls, as an unnecessary form in the settlement of ministers, he moved and carried a resolution of the Assembly of 1782, (relative to certain overtures on the subject, then under the discussion of the house,) "declaring, that the moderation of a Call in settling ministers, is agreeable to the immemorial and. constitutional practice of this church, and that it ought to be continued:" a resolution which was afterwards converted into a declaratory act, and printed as such in the proceedings of the Assembly for that year.

But what chiefly engaged his mind, and occupied his time, after he became a minister of Edinburgh, was the execution of his last and greatest work on the Apostolical Epistles; which was published in 1795, in four volumes quarto. Respecting this work, it is perhaps not unworthy of being told, that it was the result of the unremitting labour of almost thirty years; that, notwithstanding his numerous professional avocations, the author, while composing it, was seldom less than eleven hours every day employed in study; and that before it came to the press, the whole manuscript had been written no less than five times with his own hand.--At the time of publishing "The New Translation of the Apostolical Epistles, with a Commentary and Notes," Dr Macknight was highly indebted to the patronage of the duke of Grafton; and after the work made its appearance, he received the most honourable testimonies of approbation from many of the bishops and respectable dignitaries of the church of England, as well as from the ablest divines of all descriptions.

After the publication of this work, Dr Macknight considered himself as having accomplished the greatest object of his life; and, wishing to enjoy at the end of his days, some relief from the labour of study, he resisted the repeated solicitations of his friends, who earnestly urged him to undertake the illustration of the Book of the Acts, on the same plan which he had so successfully followed in explaining other parts of the New Testament.—But soon after this period, from the want of their usual exercise, a sensible decline of his faculties, particularly a failure of his memory, was observed by his family. This fact is a striking instance of the analogy between the powers of the body and those of the mind, both of which suffer by inaction; and it furnishes a useful caution to those who have been long habituated to any regular exertion of mind, against at once desisting entirely from its usual efforts; since the effect, in the course of nature, is not only to create languor, but to hasten the progress of debility and failure.

As yet, however, (1796,) Dr Macknight’s bodily vigour seemed to be but little impaired. In early life, he was afflicted with frequent headachs; but after, he had reached the age of thirty, they seldom returned: and he afforded a singular instance of a sedentary life long continued, with hardly any of those complaints which it usually induces. This uninterrupted enjoyment of health he owed, under Providence, to a naturally robust make, and a constitution of body uncommonly sound and vigorous, along with regular habits of temperance, and of taking exercise, which he did by walking nearly three hours every day.

Having finished the task he had prescribed to himself as an author, he mingled frequently in the society of his friends, from which, at intervals, he had always received much enjoyment; and long retained the same cheerfulness of temper, for which at the hours of relaxation from severe study, he had been remarkable, when in the company of those whom he esteemed. Even after the symptoms of his decline were become visible, (1798,) his natural sagacity and strength of judgment, as well as his extensive and familiar knowledge of the Scriptures, were still to be discerned in his conversation and public appearances. And so habitual was his anxiety to discharge his duty, that he insisted on officiating for a considerable time after his friends had wished him to withdraw from public labour. It was not, indeed, without much entreaty, that he at last consented to accept the services of an assistant.

The disease which terminated his life was the peripneumonia notha, occasioned by an incautious exposure to the severity of the weather, about the end of December, 1799. This distemper, in its progress and issue, resisted the ablest and most assiduous efforts of medical skill.—During his illness, his mind was composed, tranquil, and resigned; he never complained; and on the morning of the 13th of January, 1800, he expired without a struggle. As in the course of the preceding night he slept but little, the time was employed in hearing passages from the Psalms and Evangelists, which by his own desire were read to him by one of his family.—Thus, having spent his life in illustrating Scripture, and exerted the last efforts of his attention in listening with delight to its precious words, he may be truly said to have slept in Jesus.

As a clergyman, the sentiments and conduct of Dr Macknight were equally characterized by consistency and propriety. In the discharge of every public and private duty of religion, with a constant reliance on divine aid, he was regular and steady. He knew and felt what became the sacred office which he held; and never departed, on any occasion, from the dignity or decorum of his professional character. Having given himself wholly to the meditation of divine things, he continued in them: in the work of his Master he was steadfast and faithful to the end.—His piety was at once sincere, rational, and without ostentation. To be useful in the cause of truth and virtue, was his highest ambition; and with all the means of attaining this end which the resources of a well-informed and liberal mind could supply, he united a zeal for the interests of Christianity, which terminated only with his life.

When engaged, either in private controversy or in the public debates of the church courts, he was always remarkable for speaking strictly to the point at issue. He was likewise distinguished by coolness, discretion, and command of temper; he listened with patience to the arguments of his opponents; and in delivering his opinions, he showed himself uniformly open, candid, and explicit. At the same time, his talent was rather that of business than of address; he appeared to be better fitted for deciding on the merits of a question in debate, than for soothing the passions, or managing the humours of mankind,—a qualification rarely possessed but by minds of a superior order.

On various subjects, besides those embraced by his profession, his range of knowledge was ample and profound. He perused the writers of antiquity with critical skill; and of his acquaintance with the Greek language, especially the original of the New Testament, his observations on the force of the particles, in his Commentary, are a sufficient proof. In the speculations, also, of metaphysical, moral, and mathematical science, he was a considerable proficient. The fact is, his powers were such as might have been turned with advantage to any department of knowledge or learning.

It may further be noticed, that in conducting the ordinary affairs of life, he displayed uncommon prudence and sagacity. He was one of those who are generally attentive to small concerns, but on proper occasions show themselves liberal to a high degree. Of this, different instances occurred in the course of his transactions with his friends; and he was enabled to act on such a principle of generosity, by his usual habits of economy and prudence.--Dr Macknight’s external appearance was sufficiently expressive of his character. His countenance was manly and commanding, and his gait remarkably erect and firm.

Dr Macknight’s "Harmony of the Gospels" has long been esteemed a work of standard excellence for the students of evangelical knowledge. His "Truth of the Gospel History" has hitherto attracted the notice of the public less than any of his other productions; but it well deserves to be more generally read; since of what it proposes to establish, it contains the most satisfying views that can be suggested by learning, acuteness, and good sense, and is admitted by the best judges to be a performance as useful and instructive as any we have on that important subject. It is, in fact, a kind of storehouse, from which subsequent writers on the same subject, have borrowed largely in point of argument and illustration.

The "Commentary on the Apostolical Epistles" is now held in peculiar estimation; and it may be doubted whether the scope of the sacred authors of these writings was ever, in any former age of Christianity, more fully, clearly, and happily stated, than has been done by Dr. Macknight, in the general views and illustrations which he has prefixed to the several chapters of the Epistles.

The Life of the Apostle Paul, which concludes the fourth volume of "The Translation and Commentary," is an excellent compendium of the apostolical history, and may be considered as the author’s view and illustration of the Acts of the Apostles—the only part of the New Testament writings (besides the Revelation of St John) to which the labours of Dr Macknight, as a commentator, were not directed.—In all his writings, his style, though unambitious of elegance or ornament, is perspicuous, and appropriate to the subject.

All Dr Macknight’s works were originally printed in quarto. Of the "Harmony" and the "Epistles" many editions have since been published in octavo. To show the respect which has been paid in England to his various works, the following passage from the "Library Companion" of the Rev. T. F. Dibdin, may be quoted. After recommending to the young theologian the works of Lardner, Doddridge, and Watts, Mr Dibdin says, "Nor let the name of Macknight be forgotten. His works, indeed, are the more exclusive property of the disciplined theological student; but the general reader will do well to secure his inviting quartos upon the Gospels and Epistles of the New Testament. In these he will find learning without pedantry, and piety without enthusiasm. In short, no theological collection can be perfect without them. If any man may be said to have exhausted his subject, it is Macknight."