John, a celebrated critic, was the son of a respectable tradesman in London, and born in the year 1657. He received the first branches of education at the great school of Harrow on the Hill, where he commenced acquaintance and intimacy with many young noblemen and gentlemen who afterwards made a considerable figure in public affairs. By these means he laid the foundation of a very strong and extensive interest, which, but for his own fault, might have been of infinite use to him in his future life. From Harrow he went to Caius College, Cambridge, where, as soon as he was of proper standing, he took the degree of bachelor of arts. When he quitted the university, he made the tour of Europe, in the course of which he conceived such a detestation of despotism, as confirmed him still more in those Whig principles which he had from his infancy imbibed.

On his return to England, he became early acquainted with Dryden, Wycherly, Congreve, and Southern, whose conversation, inspiring him with a passion for poetry, and a contempt for every attainment that had not in it something of the belles lettres, diverted him from the acquisition of any profitable art, or the exercise of any profession. This, to a man who had not an independent income, was undoubtedly a misfortune. However, his zeal for the Protestant succession having recommended him to the patronage of the Duke of Marlborough, through that nobleman he obtained a place in the customs worth L120 per annum. This he enjoyed for some years, till, from profligacy and want of economy, he was reduced to the necessity of disposing of it to satisfy some very pressing demands. By the advice of Lord Halifax, however, he reserved to himself, in the sale of it, an annuity for a term of years; which term he outlived, and hence, in the decline of his life, he was reduced to extreme necessity.

The following is an instance of the whimsical idea he had of his own importance:—In 1704 appeared his favourite tragedy Liberty Asserted; in which there were so many strokes against the French nation, that he thought they were never to be forgiven. He had worked himself into a persuasion that the king of France would insist on his being delivered up before consenting to conclude a peace; and, full of this idea of his own importance, when the congress was held at Utrecht, he is said to have waited on his patron, the Duke of Marlborough, in order to desire that no such article might be stipulated. The duke told him that he had really no interest then with the ministry; but that he had made no such provision for his own security, though he could not help thinking he had done the French as much injury as Dennis himself. Another story relating to this affair is, that being at a gentleman's house on the coast of Sussex, and walking one day on the sea-shore, he saw a ship sailing, as he fancied, towards him. He instantly set out for London, in the fancy that he was betrayed; and congratulating himself upon his escape, gave out that his friend had decoyed him down to his house in order to surrender him up to the French.

Dennis, partly through a natural peevishness and petulance of temper, and partly perhaps for the sake of procuring the means of subsistence, was continually engaged in controversy with his contemporaries, whom he always treated with the utmost severity; and though his observations were sometimes judicious, yet he conveyed them in language so scurrilous and abusive as destroyed their intended effect; and as his attacks were almost always on persons of abilities greatly superior to himself, as Addison, Steele, and Pope, their replies usually turned the popular opinion so strongly against him, that, by irritating his testy temper, they rendered him a perpetual torment to himself. Pope has pilloried him in the Dunciad and in the following epigram:—

Should Dennis publish you had stab'd your brother, Lampoon'd your monarch, or debauch'd your mother; Say, what revenge on Dennis can be had? Too dull for laughter, for reply too mad: On one so poor you cannot take the law; On one so old your sword you scorn to draw; Unseal'd then let the harmless monster rage, Secure in dulness, madness, want, and age.

At length, after a long life of vicissitudes, disappointments, and turmoils, rendered wretched by indiscretion, and hateful by malevolence, he was compelled to submit to the degrading humiliation of receiving obligations from those whom he had been continually reviling. In the very close of his days a play was acted for his benefit at the little theatre in the Haymarket, through the united interests of Thomson, Mallet, and Pope; the last of whom, notwithstanding the gross manner in which Dennis had calumniated him on many occasions, interested himself very warmly in his behalf, and even wrote an occasional prologue to the play, which was spoken by Cibber. Not long after this, on the 6th of January 1733, the unfortunate man died, in the seventy-seventh year of his age.