When he had attained the age of seven years, his mother removed with him to Aberdeen, where he obtained the earlier part of his education. In 1703 he procured the situation of tutor to the young lord Keith and his brother, and in this employment he remained till 1710, when he was admitted to the order of deacons in the Scottish episcopal church, by Haliburton, (titular) bishop of Aberdeen; and in November following became domestic chaplain to Charles, earl of Errol, and his mother, the countess. Two years after, he accompanied his lordship to the baths of Aix-la-Chapelle, and had thus an opportunity of visiting some of the most celebrated towns and cities of the continent. Leaving the earl at Aix-la-Chapelle, he returned to England and landed at Dover, where he was compelled to remain for several months, in consequence of a severe illness, brought on by exposure during a violent storm which he had encountered in crossing the channel. On recovering sufficiently to enable him to undergo the fatigue of travelling, he set out for Edinburgh, where he arrived in February, 1713. He was shortly after this invited by a congregation of Scottish episcopalians in that city, to become their minister, and was accordingly raised to the priesthood by bishop Haliburton, on the 26th May, in the year just named. His talents and learning had already attracted some notice, and had procured for him a considerable degree of influence in the church to which he belonged, and of which he was always a steady, zealous, but rational supporter; for, although firmly attached to the faith in which he was educated, he was yet extremely liberal and tolerant in his religious sentiments. In June, 1727, he was raised to the episcopate, and was consecrated in Edinburgh by bishops Miller, Rattray, and Gadderar. He was, at the same time, intrusted with the superintendence of the district of Caithness, Orkney and the Isles, and in 1733, was preferred to that of Fife.

For upwards of twenty years after this period, bishop Keith continued to exercise his duties in Edinburgh, filling a respectable, if not a dignified place in society, and employing his leisure, it would appear, chiefly in the compilation of those historical works which have transmitted his name to posterity. In a manuscript memoir by Mr Murray of Broughton, secretary to prince Charles Stuart—which the present writer has perused—it is clearly signified that, previous to the insurrection of 1745, the bishop corresponded on subjects relating to his depressed and suffering communion, with the court of the Pretender, and that the latter personage, as the supposed head of a supposed church, gave the congé d’ elire necessary for the election of individuals to exercise the episcopal office.

The first historical work published by the bishop, appeared in 1734, in a folio form, under the title of a "History of the Affairs of Church and State in Scotland, from the beginning of the Reformation in the reign of James V., to the retreat of queen Mary into England." Though tinged here and there with high-church prejudices, the original narrative is a useful, and, upon the whole, a candid record of a very controverted part of our history; while the state documents quoted in the body of the work and at its close, have proved of incalculable service to every later writer upon the same subject. The list of subscribers prefixed to this work is highly curious, as being an almost complete muster-roll of the Jacobite nobility and gentry of the period: among the rest is the famous Rob Roy. In 1755, the bishop published his well-known "Catalogue of Scottish Bishops," which has also been a mine of valuable knowledge to later writers. The latter years of this venerable person appear to have been spent at a villa called Bonnyhaugh, on the banks of the water of Leith, which belonged to himself. Here he died on the 20^th of January, 1757, in the seventy-sixth year of his age. He was buried in the Canongate church-yard, a few feet from the wall on the western side, where a plain tomb-stone, inscribed simply with his name, has recently been erected.

Besides his eminent qualifications as an historian and antiquary, the subject of this notice possessed those of an acute and pains-taking genealogist, a study to which he was probably directed by the high value which he always attached to the dignity of his own descent, and which he was at much pains to establish. An instance of his tenacity in this particular, and of his peculiar talent for genealogical research, was exhibited in a dispute into which he entered with Mr Keith of Ravelstone, on the subject of the comparative proximity of their several families to the house of the earls Marischal.

On that occasion he printed a "Vindication of Mr Robert Keith, and of his young grand-nephew Alexander Keith, from the unfriendly representation of Mr Alexander Keith, jun. of Ravelston." In this vindication he not only succeeded in establishing his superior claims to the particular honour in dispute, but showed that he was also related to the dukes of Douglas and Hamilton. His reason for being at so much pains in vindicating the nobility of his descent, is thus spoken of in the document above alluded to: "For although he him-himself, (he speaks in the third person,) now in the close of the seventieth year of his age, and having only one daughter, might be pretty indifferent about any thing of this nature, yet he suspects his young grand-nephews, (for there are no less than three of them, Alexander, Robert, and John,) when they came of age, might reproach the memory of their uncle, and justly perhaps, for his not endeavouring to set their birth at right against so flagrant an attack, seeing the one was capable, and the others might not have the same means of knowing, or the same abilities to perform it."