Thomas, a celebrated naturalist, was born in Flintshire, about the year 1726. His family had their residence in that country for several hundred years; and he himself informs us that he acquired the rudiments of his education at Wrexham, whence he was sent to Fulham. Not long after this he went to the university of Oxford, where his progress in classical knowledge was very considerable, after which he turned his attention to the study of jurisprudence; but it is nowhere said that he ever followed the law as a profession.

We are informed that his taste for natural history, by his knowledge of which he afterwards became so conspicuous, was first excited by the perusal of Willughby's Ornithology, a copy of which had been sent him in a present. He began his travels at home, which was certainly the most proper step, to acquire a knowledge of the manners, curiosities, and productions of his native country, before he attempted to delineate those of any other nation. He then visited the Continent, where he acquired additional knowledge respecting his most favourite studies, and became acquainted with some of the most celebrated literary characters which that period produced. When he returned home he married, and had two children; but he was thirty-seven years of age before he gained possession of the family estate, after which he took up his residence at Downing.

On the death of his wife he again set out for the Continent, where he became acquainted with Voltaire, Buffon, Pallas, and other eminent characters. Being an author as early as the year 1750, when only twenty-four years of age, he had acquired a considerable degree of reputation in that capacity by the time he became acquainted with the above-mentioned philosophers. His reputation as a naturalist was established by his British Zoology, in four volumes 4to; and still further increased by his epistolary correspondence with no less a personage than Linnaeus. He undertook a tour to Cornwall at an early period of life, and also felt an irresistible propensity to survey the works of nature in the northern parts of the kingdom. For this purpose he set out for Scotland in 1771, and published an amusing account of his tour, in three volumes 4to, which was destined to receive such a share of public favour as to pass through several editions. His Welsh tour was published in 1778, and his journey from Chester to London in 1782, in one volume 4to. About the year 1784 appeared his Arctic Zoology, a work which was very much esteemed, both in his own and in many other countries. He also gave the world a natural history of the parishes of Holywell and Downing, within the latter of which he had resided during more than fifty years. Not long before his death appeared his View of Hindustan, in two volumes 4to, to undertake which, it seems, he had solicitations from private friends, as well as the wishes of persons entirely unknown to him, which were expressed in the public prints. This was unquestionably a very bold attempt in a man who was turned off seventy, a period at which the faculties of the mind must certainly be impaired, especially when exerted with vigour for such a number of years before. Notwithstanding his great age, however, the work is executed in an able manner, bearing a strong resemblance to the introduction of his Arctic Zoology.

He also published a letter on the earthquake which was felt at Downing in Flintshire, in the year 1753; another which was inserted in the Philosophical Transactions in 1756; his Synopsis of Quadrupeds in 1771; a pamphlet on the militia; a paper on the turkey, and a volume of miscellanies.

Pennant was enabled to exhibit the greatest hospitality at his table, in consequence of the ample fortune which had been left him at his father's decease; and he gave the profits arising from the sale of several publications to charitable endowments. By his generous patronage a number of engravers met with great encouragement, and he contributed not a little to the promotion of the fine arts. About the age of fifty he married for the second time, a Miss Mostyn, sister of his neighbour, the late Sir Roger Mostyn of Flintshire. The concluding part of his life was cheerful, and it may be affirmed that he scarcely felt the advances of old age. He died at his seat at Downing in 1798, in the seventy-second year of his age.

Pennant inherited from nature a strong and vigorous constitution; his countenance was open and intelligent; his disposition was active and cheerful; and his vivacity, both in writing and conversation, made him perpetually entertaining. His heart was kind and benevolent, and in the relations of domestic life his conduct was highly worthy of imitation. The distresses in which his poor neighbours were at any time involved gave him unfeigned uneasiness, and he endeavoured to relieve them by every means in his power. He was possessed of candour, and free from common prejudices, a truth fully evinced in all his publications. The people of Scotland were proud to confess that he was the first English traveller who had fairly represented their country, in its favourable as well as in its less pleasing appearances. His style is lively, and fitted to convey the ideas which he intended to express, but it is not always correct. In zoology his arrangement is judicious, and his descriptions characteristic. If we discover several traces of vanity in those works which he published near the close of life, it ought to be remembered that it is the vanity of an old man, which is seldom disagreeable, especially when united with amiable manners and a benevolent disposition.